The AskCIDD program is no longer actively taking questions from the public.
During the first year of the COVID-19 pandemic, the Center for Infectious Disease Dynamics created the AskCIDD program to answer the public's questions about the disease. A team of more than 50 Penn State researchers, led by Elizabeth McGraw and Nita Bharti, responded with answers informed by the best science available at the time. Some of those answers were revised and updated as new, more complete information became available.
To review our answers to the most popular questions submitted during the first year of the COVID-19 pandemic, you may peruse the list below or visit the AskCIDD video playlist on YouTube.
Thanks and Be Well,
The answers to the questions below were last updated in June 2022:
Because the vaccines being developed are based on an immune response against multiple sites on virus surface proteins, they have been largely effective against small amounts of genetic variation globally in SARS-CoV-2 isolates. However, as the virus has continued to evolve, the efficacy of the vaccine may be reduced for some variants. Long-term first-generation vaccines may need to be revised and replaced to cater for growing diversity in the virus.
Getting a flu shot is important every year because it directly protects you from getting infected with influenza, which can be really miserable while you’re sick, but can also be fatal. A flu shot also indirectly protects your contacts – since you’re less likely to get infected after getting immunized, you’re also less likely to infect your friends and family.
Getting a flu shot this year is particularly important because, like SARS-CoV-2, influenza is a respiratory virus and we want to do everything we can to minimize having two respiratory outbreaks circulating simultaneously in our populations. We don’t know what co-infection or sequential infections for these two viruses looks like, but we worry that infection with one could increase the severity of the other. It’s also possible that infection with one could weaken the immune system and increase susceptibility to the other. A small study from China indicates co-infection may increase the infectious period for COVID-19 and prolong hospital stays (2). Last year in the US, before COVID, the CDC estimated that influenza infections sent around 500,000 people to the hospital (1). If flu vaccine coverage this year is only about the same as last year, the compound effects of influenza and COVID could quickly overwhelm local health care systems. The more people who get their flu shot this year, the more cases of influenza we can prevent.
Another reason to get a flu shot this year is because both SARS-CoV-2 and Influenza are respiratory viruses with similar early symptoms. Experiencing symptoms of flu could lead patients to seek COVID testing. Increasing immunization levels against influenza will help reduce flu infections and avoid needless COVID testing. On the other hand, mistakenly thinking cases of COVID-19 are due to influenza might lead to insufficient isolation periods and increased transmission of SARS-CoV-2.
The social distancing, hand washing, and mask-wearing that we’re all getting really good at to prevent COVID-19 should also be protective against influenza. Flu season in the northern hemisphere begins around November, so you’ll benefit from scheduling your flu shot before then.
Some people are concerned about the safety of the new COVID-19 vaccines due to the speed at which they were developed.
This is a very fast timeline for a vaccine. The speed has been gained by intentionally making the process as time efficient as possible, not by eliminating steps from development, production, or safety and efficacy assessments. Many steps that would normally be run sequentially, were instead run in parallel, including trials and production (figure 1 https://www.nature.com/article... ).
The Moderna and Pfizer mRNA vaccines will be the first ones available. The advantage of RNA vaccines is that they provide the instructions for the recipient to make a harmless protein that triggers the protective immune response we want. They are also faster to make than traditional vaccines.
The safety and efficacy trials for these mRNA vaccines included 30,000 and 44,000 participants in each, respectively. Half of the participants in each trial received the vaccine and other half received a placebo. Based on the frequency of adverse effects between the two groups in each trial, both vaccines were determined to be safe. The safety monitoring board and the FDA made their approval decisions after considering two months of follow up safety data. And based on the number of participants who reported symptoms of COVID-19, the vaccines were both shown to be highly protective against disease, particularly against severe disease.
As the mRNA based vaccines have been used in large numbers globally, we are not seeing any issues with safety.
Public Health Questions
First this is a new virus. That means our bodies have not seen this virus before and we are unlikely to have any antibodies. This virus seems to be spreading through the human population much faster than flu, and part of that has to do with the fact that all of us are susceptible. With the flu, most of us are carrying some level of antibody protection from a previous year’s exposure or from a vaccine. Additionally, the case fatality rate is estimated to be 10 times higher for COVID-19 that the flu. Lastly, this virus is new to medical personnel, too. They are learning how best to both take care of patients and possibly treat it.
Given that the novel Coronavirus is a respiratory transmitted virus, we expect that at some point there will be season patterns of transmission, rising in frequency in the colder months just like flu. Because the virus is just sweeping through populations however and people are highly susceptible it may not behave in this predictable manner initially. Additionally, we will first need to see how the virus spreads through the summer months. That pattern will be dependent on a range of factors including transmission in warmer/humid weather, the degree of immunity in the population and our level of physical distancing.
During an epidemic, you’ll hear epidemiologists talk about the Case Fatality Rate. The Case Fatality Rate is the proportion of total cases that results in fatalities. This is a population level measurement. With this coronavirus pandemic, we know there are asymptomatic cases, which aren’t diagnosed, as well as symptomatic cases that aren’t diagnosed due to a lack of testing. This means that our records are incomplete for both the denominator – which is the total number of cases – and the numerator- which is the total number of COVID deaths. These numbers are currently skewed towards identifying symptomatic cases and, severe cases, which are more likely to have negative outcomes. Model estimates have tried to account for those biases. For this pandemic, it’s not terribly important for everyone to know a precise number for the case fatality rate, it is more important to realize that even a low case fatality rate in a fully susceptible population like ours, will cause a lot of deaths. You can help reduce these numbers by continuing to reduce transmission. Follow your local current guidelines on masking and testing. Stay home when you are sick.
To figure out where we are in the progress of an epidemic while it’s happening, epidemiologists plot the number of new cases per day, which is called the epidemic curve. You’ve been seeing these plots for coronavirus at national levels, for your state, your county, and maybe your town. During the period when the number of new cases per day is increasing, we are in a time before the peak of the epidemic. When the number of new cases per day begins to consistently decrease, we assess that we might be past the peak. It’s not really possible to define the true peak until after the epidemic is over. Even after cases have started to decline, there’s always a chance that they could rise again once control measures are lifted. For this particular virus, we know there are lags in reporting and an incubation period, so the cases reported today represent infections that were acquired sometime in the past two weeks. It’s important for epidemiologists and policymakers to keep an eye on these epidemic curves to assess the interventions put in place and update them as frequently as necessary.
Patients with existing respiratory condition are at risk for developing more severe cases of COVID-19. There are a lot of factors that can contribute to respiratory conditions, including genetic factors, behaviors - like smoking, and environmental characteristics, like air quality. A lifetime of inhaling air that is polluted with particular matter or irritating gasses can exacerbate existing respiratory conditions. And, even in healthy people, inhaling particulate matter, nitrogen dioxide, or ozone can damage or irritate airways. This may contribute to the likelihood of infection upon exposure or the severity of disease upon infection.
However, we can’t quantify the direct impact of air pollution on COVID-19. In many areas with high levels of air pollution and large outbreaks of COVID-19, we also see a number of confounding factors, like high population density, which leads to increased transmission between people and larger outbreaks.
In the wake of large-scale coronavirus related shutdowns in manufacturing and movement, we’ve seen noticeable improvements in air quality. As we develop ways to incorporate these activities into our new COVID-resilient communities, it is reasonable to think that efforts to maintain cleaner air will contribute to health improvements in a number of ways.
This is a difficult question to answer. In controlled studies where cross sections of the population were screened for SARS-CoV-2, regardless of whether they had symptoms, it appears that 25-50% of the population has no symptoms during the course of their illness that would make them think they had COVID-19. This is different from pre-symptomatic individuals, that are capable of transmitting but may begin to show symptoms in a few days time. So, when a state reports say 70,000 cases, most of those are going to be from symptomatic individuals who sought care and testing. Some proportion will likely be asymptomatic – but only in situations where people sought tests despite feeling well, likely because they were exposed to a known positive case or because routine testing was part of their workplace. This means that the numbers of reported cases are likely a massive underestimate of the actual numbers of cases, particularly asymptomatic individuals. Widespread testing for antibodies, once the accuracy of these tests is assured, will ultimately reveal the true numbers of cases that were present in a population and the proportion that were asymptomatic.
Models are always wrong for two reasons: abstraction and influence. However, mathematical models of diseases can be extremely useful and informative when trying to understand how a disease may spread or how a particular intervention strategy may impact that spread. But it’s critical to understand a model’s design and purpose to be able to interpret it correctly. In other words, let’s quickly break down an often cited quote that is attributed to British statistician George Box, “All models are wrong but some models are useful.”
The first thing to know about all models is that they are designed as abstractions of reality. They are meant to represent only some parts of reality so they are intentionally reductive. No model includes every single element of the real world; doing so would be both impossible and would render the model useless. What a model includes and leaves out is based on what it is designed to accomplish. In general, ‘useful’ models are designed to identify the underlying mechanisms or processes that give rise to outcomes – whether it’s disease transmission, the adoption of protective behaviors, vaccine uptake, or any other important factors in a disease outbreak. By identifying the critical elements and understanding their interactions, models can help us learn how to manage and mitigate outbreaks. Even if a model incorrectly projects the size of an outbreak or the rate of its increase, that model may be incredibly useful for identifying critical contributing factors to the spread of a pathogen and assist in management and prevention.
The other reason that models are always wrong is because models can influence policy makers, intervention strategies, and individual behaviors. In doing so, models can incite changes that alter outbreak trajectories. If a model reveals paths of action that can save lives or prevent disease, those actions are often taken. The end result would be fewer cases than the model predicted, meaning the model was ‘wrong’ in its predictions but it was extremely useful.
Every disease model is a reductive abstraction of reality. Many models provide insights that help reduce or prevent morbidity and mortality.
Understanding the protests in the context of the pandemic is important.
Both the pandemic and police brutality, along with countless additional forms of systemic racism and inequality, are disproportionately killing Black Americans. They are equally serious symptoms of underlying systemic inequality. They are imminent threats to the health and safety of Black Americans.
Did you know?
COVID-19 has disproportionately sickened and killed Black residents in America. High density housing in urban areas aided transmission, reduced access to health care allow infections to simmer, and continued essential work increases exposure. The novel coronavirus caused more than 1.5x as many Black deaths (per 100,000 population) than white or Asian deaths as of March 2021.
At the same time, today in America, unarmed Black men are more than twice as likely to be killed by police than white men (per 100,000 population).
Racial inequities in health and justice are both serious issues that require urgent attention and systemic solutions. Protestors are fighting to address both of these issues, and many more.
Following a few months of quarantine, protesting presents an increase in social contacts, which increases participants’ risk of exposure and transmission of SARS-CoV-2. To protest as safely as possible, wear a mask, ask others to wear masks, and don’t touch your face. Keep hand sanitizer with you and use it frequently. Avoid face to face interactions or conflicts and do your best to maintain a six foot radius of physical distance, though we know this can be difficult. Incorporate noisemakers or percussion instruments to reduce your shouting or chanting, which can forcefully release respiratory droplets containing virus.
Luckily, protests are outdoors, which mitigates transmission, and presents a significantly lower risk of transmission than indoor activities or sustained interactions.
We encourage people to be informed. Everyone needs to decide for themselves what level of risk they are comfortable with. People who can’t participate in protests for any reason but want to support the Black Lives Matter movement can be involved in a number of ways, from monetary donations to reading and learning about the breadth of racial inequities in America and their widespread negative outcomes, and most importantly, voting.
Many bars and restaurants have re-opened their doors. However, this does not mean that they are safe. Many new clusters of infection have been traced back to dining and drinking experiences. These activities are particularly risky because a mask can’t be worn while eating or drinking. If you are recently vaccinated your risk will be lower than if you are unvaccinated. Outdoor seating offers high protection due to increased air flow. Takeout is also a great, safe option for supporting local businesses and enjoying your favorite foods.
Gyms continue to pose a risk for the spread of COVID-19, especially for the unvaccinated.
Fitness classes, studios, and indoor gyms present a unique risk to instructors and attendees. Countries that had very effective control measures and have been able to reopen are providing valuable information. With very high levels of surveillance and testing, many resurgences in cases and outbreaks have been linked directly to fitness activities. After reopening in May, Japan traced clusters of cases back to gyms. A well-documented example with careful contact tracing highlighted how a fitness studio in South Korea spread the virus amongst its instructors and members.
These outbreaks have confirmed our suspicions that the virus transmits effectively during fitness activities, when people exhale and inhale forcefully. This allows the virus to travel farther in respiratory emissions during physical exertion than it does during normal breathing and speaking. This is true indoors and outdoors but the effects on transmission are magnified indoors. Some gym’s may require masks to reduce transmission. You may also opt to wear a mask for your own protection.
Small, outdoor fitness and dance classes with significant spacing between participants present a relatively low risk of transmission.
Indoor activities with few participants and little interaction (physical contact, face to face conversations) present a risk but, depending on the facility and the number of users, it may be manageable with drastically reduced capacity, improved ventilation, and frequent cleaning of all surfaces and equipment.
Activities that involve direct contact between members from different households present a very high risk of transmission. This includes activities like partner yoga and any training that involves sparring with someone.
Gyms will be safer when there are very few local cases, so it’s important to be aware of and responsive to what’s going on in your area.
Herd immunity is the concept that some susceptible individuals in a population can receive indirect protection from an infection if they mostly come into contact with people who are immune to the infection. The more immunity there is in a population, the fewer susceptible people there are, and the more likely they are to have this indirect protection.
The threshold level of immunity in a population required to actually break chains of transmission and eliminate a pathogen from a population depends on the reproductive number of the pathogen, or how well it transmits between people. For a virus like measles, which is one of the most infectious human pathogens, the proportion of the population that must be immune to the virus to protect the susceptibles is somewhere around 95% of the total population, which is very high. For a virus like SARS-CoV-2, which causes COVID-19, that proportion is around 66%, and while that’s lower than it is for measles, it’s still very high.
With large numbers of people in the US (and around the globe) still unvaccinated the virus has continued to circulate and also mutate. The immunity provided by the vaccines is not perfect against several of the new variants, although it reduces the incidence of severe disease.
Another way we can indirectly protect susceptible individuals from infection is to reduce the number of infections and infectious individuals in the population. We can do this with behavioral interventions, by reducing contacts, and by maintaining physical distance when we’re outside out household. All of those things will reduce the number of infections and infectious people in our population and will help protect susceptible individuals.
Social Distancing & PPE-Related Questions
If you’re unwell or if you have any reason to suspect you may have been exposed, even if you feel fine, don't go out. Don't’ go anywhere. Stay home, monitor your symptoms, and isolate yourself. Have a friend, neighbor, or delivery service drop off necessities in front of your door.
If you have had no suspected exposure to the virus and you have no symptoms, you can go shopping yourself. Limit the number of trips you make, so buy enough for a week or two. Be very deliberate and surgical about it: Make a list, go the store, get what you need, come home, and wash your hands. Use the self-checkout if you can. Wash your hands and don't touch your face.
As long as you’re feeling healthy and don’t think you’ve been exposed to the virus, going for a walk is an excellent idea. Fresh air and a change of scenery will lift your spirits. However, the rules of physical distancing still apply. Don’t get close to people and maintain your six feet of separation. We’re seeing some cases where people are advised to go out to parks and then the parks become crowded and have to close. So go outside but only if you can maintain responsible distance from others.
How do we share outdoor space responsibly? If you’re walking, running, or biking side by side with someone, follow the usual rules: six feet of distance.
If you’re behind someone who is walking, running, or biking, the guidelines are a little different. A preliminary study by aerodynamicists using simulations of microdroplets in saliva left behind by a walker, runner, and cyclist shows that your best bet is to stay out of the slipstream, also know as their draft. In other words, to minimize your risk of exposure to viral particles from an athlete ahead of you, avoid drafting. Drafting involves placing yourself directly behind someone to reduce wind resistance. If you’ve been intentionally drafting to gain a competitive advantage, you should stop for now. The study says that to avoid the slipstream of someone directly in front of you, you need to keep a distance of about 5 yards between you and someone walking ahead of you, about 10 yards between you and someone running ahead of you, and a staggering 20 yards between you and someone cycling ahead of you.
If you don’t have quite that much space, you can drastically reduce your risk of exposure by staggering your position, or following someone diagonally instead of being directly behind them. So if a runner or cyclist passes you, offset your position so you’re diagonally behind them, not directly behind them, and keep your six feet of distance the whole time. And if you’re going to pass someone, position yourself diagonally behind them with plenty of distance to spare. So as you approach them, you’re not in their draft.
The universal masking recommendation says that all Pennsylvanians should wear a mask anytime they need to leave their homes. Masks are good for two things: protecting other people from your respiratory droplets and protecting you from others’ respiratory droplets. If you’re going outdoors and you’re not going to see another person, even from a distance, while you’re out walking your dog, you don’t need a mask. If there’s even a chance you might see another person, bring your mask with you so that if you see someone in the distance, you have plenty of time to put it on before you’re near them.
Keep in mind that if you’re in a city or a populated area, including a college campus, you probably always need to wear a mask whenever you’re outside. This question came to us from someone in an isolated area with a lot of outdoor space.
As restrictions begin to ease, one strategy for increasing your socialization but maintaining safety is to choose to socialize with only one other family group. These quarantine ‘pods’ or ‘bubbles’ can still be relatively safe if both households are practicing social distancing. You should keep the size of the bubble small, fewer than 10 people. You can also reduce your risk in your bubble by socializing outdoors, washing your hands frequently, and wearing a mask as talking can lead to lots of expelled virus from infected individuals. If you are eating together, get people to bring their own cutlery and dishware and cool side dishes. Hot food can be served up safely directly from the grill or oven pans with utensils and people should all use hand sanitizer before they eat.
If you need to let a workman into your house, you should both wear masks and keep your distance. You can point them in the direction of the repair rather than following close behind. You can also increase air turnover in your house by opening up the windows. When they leave, you can wipe down any door handles, surfaces they interacted with. Similarly, if you are having a responsible, social distancing party in your backyard with a few people and someone needs to use the bathroom, you can let them use it. However, make sure there is a clear path to the bathroom. Set out paper towels for them to dry their hands with. Ask them to use paper towels when they touch surfaces, like the tap etc. You can also wipe down surfaces after then have finished.
After a suspected or confirmed infection, the CDC has formal guidelines establishing when it is safe for someone who has recovered from infection to leave isolation.
If you had symptoms that you think or you know you had COVID-19, you can be around other people and leave your isolation after it’s been at least ten days since your symptoms appeared and you have 3 days with no fever and an improvement in symptoms. If you can get tested, you can exit your isolation after two consecutive negative tests at least 24 hours apart, no fever, and improved symptoms.
If you tested positive for COVID-19 but you did not have any symptoms, you can be with others 10 days after you tested positive or after two consecutive negative tests at least 24 hours apart.
Just because you and your partner or roommate are both infected with the same virus does not mean you should consider interacting during any time when either of you could be infectious. Check back in the with the CDC periodically for updates to these guidelines.
For the past few months, a lot of individuals over 60 have been able to have their shopping done for them, either by family members, neighbors, or delivery services. But if that is no longer an option, there are safe ways for senior citizens to go to grocery stores.
First, check to see if local stores have specific “senior hours” set aside for grocery shopping. These are times when people under a certain age are not allowed to enter the store, the total number of customers allowed inside is very low, and they are often first thing in the morning when the store opens, right after it is cleaned thoroughly. If that is an option, seniors should absolutely take advantage of it if they are able to.
Second, take all precautions: wear a clean mask and don't touch it once it’s on and in place, use hand sanitizer frequently (many stores have dispensers placed throughout), be very conscious of maintaining physical distancing, avoid face to face interactions entirely, and definitely no face-touching. Try to follow a ‘clean hand, dirty hand’ approach. If you run into someone you know, don’t forget that we’re in a pandemic – please don’t stop and strike up a conversation. Wave and keep moving, indicate that you’ll call them later if you want to chat.
Third, stock up with about two weeks of supplies to reduce the frequency of trips.
As soon as you get home, wash your hands. Then remove your mask and wash your hands again. Put all your groceries away and then wash your hands again.
Instructors and teachers should not consider wearing only a face shield in a return to in-person instruction. To be used correctly, face shields should be coupled with face masks. Face masks that cover the nose and mouth are protective for the people around you. These can be anything from reusable fabric masks to medical-grade PPE. These kinds of masks reduce the likelihood that your respiratory droplets will reach another person and potentially infect them. Face shields are clear plastic that do not effectively prevent your respiratory droplets from reaching others. They are open at the bottom and on the sides, allowing space for respiratory droplets to reach others.
Face shields are generally used when there is danger of viral infection into the eyes or elsewhere on the face or a danger of splatter, which could penetrate or absorb into a fabric or surgical mask. In these cases, they are an additional layer of PPE that are always used WITH masks.
In an indoor classroom setting when a teacher is likely to be speaking and projecting their voice, a mask is absolutely necessary. Wearing a shield in addition to a mask is optional. Additional recommendations for educators may vary by institution but the CDC guidelines to wear a mask in public should definitely be applied to classroom settings.
When wearing a cloth mask, it is important to wear it over both your mouth and your nose. Virus particles can be expelled via the mouth when coughing, talking, singing, etc. They can also be expelled via the nose when sneezing or just breathing. Wearing a mask just over the mouth is therefore not effective in reducing your potential for infecting others with virus. If you see people with a mask down over their nose in public, you might politely let them know that “their mask seems to have fallen down from their nose.”
We’re seeing increased mask wearing, which is great, but we’re also seeing some improper mask wearing. The primary purpose of a mask is to prevent your respiratory droplets from traveling to other people. Those droplets come from your nose and mouth so your mask should cover both of these areas and the perimeter of the mask should maintain tight contact with your face. Remember, one of the ways samples are collected for diagnostic lab tests is by nasal swabs, which means the virus is present in the nasal cavity of infected individuals. An interesting recent study detailed how a pair of hair stylists that had both had symptomatic COVID-19 together interacted with 139 clients. One of the stylists infected members of her family in the home environment. In the salon, all clients and the stylists were wearing masks. Reassuringly, not one of the clients exhibited COVID-19 symptoms and 67 of whom regardless sought out a test were negative for virus.
Activities like sneezing and coughing are the highest risk events for spreading SARS-CoV-2. We know that an uncovered cough or a sneeze can spray virus containing droplets into the air over 8 feet or more. We also have growing concern that the virus can remain in the air for long periods, particularly indoors. If you are feeling unwell, with sneezing and coughing the best place for you is at home, isolated from others. If you are just worried about the occasional cough or sneeze that could still spread virus if you are an symptomatic carrier, you should wear the mask despite it being unpleasant for the wearer. You might like to keep an extra cloth or disposable mask in case yours becomes wet/soiled. As a reminder, cotton masks should be washed out at the end of the day before reuse. If you are outdoors and need to sneeze and you can get far away from people, it should be safe to remove your mask.
The answers to the questions below were last updated in January 2021:
Testing and Treatment Questions
Yes. A number of countries are currently rolling out antibody tests and the phrase ‘immunity passports’ is being used to describe how with a positive antibody test people may be free to go back to work. In the last few days the FDA approved a rapid antibody test that can be used by diagnostic labs to determine in just 2 minutes if someone has antibodies in their blood. As an important note, it can take several weeks to make strong antibodies. Once these tests are broadly available people will need to wait for several weeks after getting sick so that their results are accurate. These tests will initially be carried out on people who tested positive with a COVID-19 diagnostic test to make sure the antibody tests are accurate.
There are no known or approved effective treatments for COVID-19. Recently, the World Health Organization launched a set of multi country global trials on 4 sets of drugs to compare the severity of disease and survival of people on the drugs vs those not. One drug that has been controversial, chloroquine, has been included in these studies. The scientific community is urging caution as the original study showing potential efficacy of chloroquine + an antibiotic was based on a very few number of patients. Many of those patients were lost out of the study into the ICU, meaning they did indeed end up having severe disease, a fact not captured in the data. The FDA has not approved the use of chloroquine for COVID-19. In the coming weeks, the WHO led global studies should provide some information about treatment options. In the meantime, people taking chloroquine without evidence of efficacy are putting themselves at risk of side effects and limiting the ability for patients who take the drug for other conditions like lupus from accessing it.
You’ve all heard that the process involves collecting a sample using a nasal swab. But what happens after that? A thin swab is inserted into a patient’s nasal passage for a few seconds. It absorbs the secretions from the surrounding tissue. We use that swab to look for the virus’s genetic material. While our genetic material is stored as DNA, this virus RNA. To look for viral RNA in the sample, we first remove everything else from the sample. Proteins and fats are chemically destroyed so you’re left with only RNA. That includes RNA from the host, maybe the coronavirus, and maybe other viruses. The standard CDC and WHO tests use a process called reverse transcriptase polymerase chain reaction, or RT-PCR. The first step is reverse transcription, where the RNA is used to produce DNA. Then you add a fragment of DNA that is complimentary to a target segment of DNA for the virus. If the virus is present, the fragments will bind to the target portion of the viral DNA. The exact target varies between tests, but process is the same.
Then the DNA is amplified through a polymerase chain reaction, or PCR, which cycles through temperatures that trigger chemical reactions that copy the viral DNA. The DNA doubles in quantity with every cycle so if you started with any, you may have billions of copies of it by the end of just 35 cycles. At the end of this amplification stage, you measure how much DNA is in the sample. A negative result means there was no detectable DNA found at the end of the thermocycles. A positive result means the targeted DNA was detected.
But remember, no test is perfect. False negative results can occur if the sample is collected or transported incorrectly. They can also occur if the patient simply isn’t shedding a lot of virus at the time of sample collection. False positives can occur from sample contamination or by targeting non-unique segments of DNA, which results in the replication of a similar virus but not the target virus. Standardized kits are designed to reduce this error.
After a patient recovers and clears the virus, they will no longer have viral RNA in their nasal secretions and an RTPCR test will come back negative. These tests measure active infections only.
Antibody testing tells us how many people were previously infected with a pathogen. Beth gave us a great overview on this in an earlier video and what it might mean for individuals as we look ahead. Antibodies can be detected during infection or afterwards, even if the infection was asymptomatic and the patient never sought testing or treatment while they were infected.
An advantage of these tests is that they can tell us what’s happening at a population level – for example, what proportion of the population has likely been infected and what proportion is susceptible? Using large numbers of individuals helps overcome the errors of overinterpreting any single test result and the information can help us make public health decisions.
First, serological testing can help us understand the case fatality rate. In a previous video, I explained that the case fatality rate is the number of infections that result in death. I explained we couldn’t accurately calculate that at the moment because we don’t know how many infections there have been and we’re mostly counting severe and symptomatic cases, which tends to overestimate case fatality rates. Serological testing would help us understand the total number of previous cases better than we do now, so we can more accurately calculate the proportion that resulted in fatalities. This same information could help us estimate transmission rates across populations. Which ties in to my next point: Second, serological testing could help us measure exactly how effective behavioral interventions have been. By measuring the differences in serological findings across populations, we can assess behavioral interventions were effective and successful, and try to understand why others might have been less effective. We can use that information to update and adapt the next phase of behavioral interventions.
hile there is a lot of talk about assessing individual immunity to allow the recovered members of society take on critical tasks, we’re not quite there yet with testing accuracy.
The sensitivity of a test describes its ability to correctly identify someone who has had the disease and the specificity refers to a tests ability to correctly identify someone who has NOT had the disease. A false negative from a test with low sensitivity would be misleading, but a false positive from a test with low specificity could cost many lives. This could happen due to cross reactivity with other viruses, which is particularly important because we know other coronaviruses frequently circulate through our populations.
Ideally we would like the sensitivity and specificity of the serological tests to be near 99%, which means that tests should return only about 1 false positive and 1 false negative for every 100 true positive and true negative results.
If we know a test has a specificity of 85%, for example, we can estimate a range of immunity for a population across thousands of samples. That can tell us how many cases to prepare for in the coming months and when to ease restrictions. However, we can’t use a test with 85% specificity to clear a single individual for high risk activities without endangering a lot of lives. The currently available tests need improvement in both sensitivity and specificity before we can use them confidently to assess individual infections.
So while serological tests may not yet be accurate enough for us to make decisions about individuals, they can tell us a lot of important information about populations and making population level health policy.
As we look ahead to understanding the long term health effects in people following recovery from COVID-19, we can really only go back as far as the earliest human infections – which happened around December of 2019. We don’t know what this infection means for long term recovery with regards to tissue damage, from mild to severe cases. We know that recovery from any serious illness or stay in intensive care can be difficult. Make sure you follow guidelines for physical and emotional recovery and don't expect recovering individuals to bounce right back.
The other important unknown about long term effects following infection have to do with immunity. How long does immunity last and how strong is it? Scientists have detected antibodies in experimental animals that have recovered from the virus. Moving forward to understanding what that means for humans, we’ll have to test for antibodies, which Beth described in a previous AskCIDD video.
Pooled sample testing is an efficient and widely used strategy to test for an infectious disease in a large number of samples. Pooling samples means testing facilities combine a small amount of a sample from many samples, combine them, and then run the test to look for the virus across that combined, or pooled, sample. If a pooled sample tests positive, then sub-pools or individual samples are tested to identify the positive individual samples. If a pooled test returns a negative result, then all individual samples in that pool are negative. This is known as ‘Dorfman testing’ and it is the most widely used form of pooled testing. This strategy is particularly effective if prevalence and transmission of the disease are low in the population.
Pooled sample testing allows testing facilities to process large numbers of samples rapidly. The are three big advantages of this approach:
- First more samples can be processed in a short amount of time
- Second, this strategy reduces the total number of tests that need to be done
- Third, pooling samples reduces use of limited reagents, which are difficult to source when demand is high, like it is right now.
A study from Germany showed that pooling anywhere from 4 to 30 samples was an efficient strategy to detect SARS-Coronavirus-2 without sacrificing test sensitivity. This means they didn’t miss any positive samples in these pooled tests. Each testing facility can determine the optimal number of samples they should pool based on the sensitivity of their tests.
Pooling samples to efficiently and effectively screen a high volume of clinical samples for infectious diseases has been done for a long time. A return to basic operations for most counties and states will require a massive amount of testing because we’ll need to test asymptomatic individuals in addition to symptomatic individuals. Saving costs and time per individual test could help strategic efforts to ramp up testing.
Remdesivir is an antiviral that was first developed to use against Ebola virus. This last week, the first data from a double-blind, randomized, placebo-controlled study for use of Remdesivir against COVID-19 was published in the New England Journal of Medicine. Over 1,000 people testing positive for COVID-19 with lower respiratory symptoms were given either the drug or a placebo and followed to examine their recovery. In a double-blind study like this, the doctors/researchers are also not aware who was given the actual drug to prevent any bias in evaluating patient recovery. The study showed that those given the drug recovered on average after 11 days vs those given the placebo who recovering after 15 days. Severe disease was seen in 21 percent of patients on the drug and 27 percent of patients taking the placebo. Death rates were also slightly lower for those on Remdesivir, 7 percent vs 11 percent for the placebo. This study therefore shows some improvement in severity, death rate and duration of disease for people taking the drug. It is not however an instant cure. Additional studies may yield further information on dosing strategies and use in different types of patients.
In a previous week, we explained that pooling samples is an efficient way to test a lot of samples at once and it can be particularly effective when prevalence is low. This strategy allows researchers to rapidly and cheaply test a lot of samples. In the US, pooled testing is often used in testing for a number of sexually transmitted infections and when screening blood donations for diseases.
So are people actually doing this during the current COVID-19 pandemic? Yes and no. Pooling samples helped diagnostic labs in Wuhan, China rapidly scale up the number of tests they could process per day.
For COVID-19 diagnostic testing in the US, all protocols or changes to protocols must be approved by the FDA. Pooling samples is a change to the standard protocol. Some labs and some tests are approved for pooled testing under an emergency use authorization. So the technical answer is yes, in the US testing pooled samples has begun in a few provisional labs but it’s not yet being done widely.
Unfortunately, the answer is yes, for several reasons. First, we know that if you take the antibody test too early after getting sick, your body won’t have had sufficient time to have made antibodies. It is recommended that you wait several weeks after falling ill before getting an antibody test. A recent study has also revealed that people who have asymptomatic cases of COVID-19 only continue to produce antibodies for a short period of time. So, it could be that your infection was not strong enough to trigger a lasting antibody response. Third, there are many versions of antibody tests being used, many of them appear to perform very poorly. We know this because we see high rates of negative results even when we test patients that previously had COVID-19 symptoms and that tested positive by PCR for the virus. This failure is likely the result of real underlying biology, ie declining antibody loads in patients, as well as technical issues around the sensitivity of the test itself.
Unfortunately, tests cannot definitively tell you if you’re infectious, or capable of transmitting the virus. Serology tests, or antibody tests, can tell you if you’ve likely been infected and had an immune response. Diagnostic tests can tell if you’re likely to be currently infected by looking for the presence of virus in your mucosal membranes. If a diagnostic test results returns positive OR you are symptomatic, it is safe to assume that you are infectious.
However, neither serology nor diagnostic tests are perfect, and they cannot tell you whether you are actively infectious or not. Due to testing errors and detection thresholds, it is technically possible to test negative for both of these tests and still be infected and infectious. The best advice is to continue to act cautiously and protect others from you, as if you are infected and infectious.
This is an area that needs further study. First, there are very few ways to broadly boost immunity. Second, we still have a poor understanding of what happens to the immune system during COVID. While it might make sense to boost immunity early on in the course of infection or in immunocompromised people, it could cause problems later on as by-products of the inflammatory response are thought to be the cause of COVID-19’s severity. This late inflammation has been called the ‘cytokine storm.’ Some researchers and doctors, however, are skeptical of such a storm, believing instead that early inflammation gives way to exhausted and non-functional T cells (immunity cells) late in the infection that have become over-run with virus. Multiple studies are underway to try to understand immunity during COVID and whether either boosting or reducing the immune response would be a good idea. A number of drugs are also being trialed. Steroids, already standard COVID treatment, reduce inflammation broadly, but more surgical approaches targeted at reducing cellular uptake of key players like interleukin 6 are also being explored. Examples of potential immune boosters include interleukin-7 that improves T-Cell proliferation and granulocyte-macrophage colony stimulating factor (GM-CSF) currently given to patients post bone marrow transplant to help rebuild their immunity. Last, many of these drugs are also being studied in combination with antiviral therapeutics like interferon.
We know that a small proportion of people may continue to test positive for SARS-CoV-2 long after they have recovered, sometimes after previously testing negative. The latter may relate to the sensitivity of the diagnostic test or the luck of whether virus, rare in the body, is captured in the sample. The good news, coming from research in South Korea, suggests that these recovered, but positive testing people, are not likely to be contagious.
It’s important to have rapid turnaround on COVID-19 tests because tests results trigger actions that are critical to outbreak management. First, it’s important for each person to know whether they are infected or not. If they’re not infected, finding out quickly will minimize the disruption to their lives and stress levels. If they are infected, they can proceed with isolation, which protects the people around them, and symptom monitoring to manage their case. Second, a positive test result will result in contact tracing to identify and notify their contacts who may have been exposed. The faster those people can be informed, quarantined, and tested, the fewer people they will potentially expose to the virus. This is currently the only way to get ahead of chains of transmission. Longer turnaround times for test results mean that infected people and their contacts can be unknowingly transmitting the virus for several additional days. In some cases, we’re seeing test results returned several days or a week after samples were collected, which almost too long to be actionable. Ideally, results would be available in a matter of hours but receiving test results even within a day or two would significantly help reduce transmission.
A recent study showed that the virus can live on hard, smooth surfaces like metal and glass for up to three days and on cardboard for up to 24 hours. So, this is why, cleaning surfaces with alcohol based cleaner, washing your hands frequently and not touching your face can help to reduce the transmission of the virus. Social distancing is also effective at limiting your contact with contaminated surfaces touched by others in public spaces. An even more recent study shows that virus can remain intact on fabric for up to two days. If you are working outside the home and having contact with lots of people, it is best to change your clothes upon arrival home, and wash them in warm/hot water. This is standard practice for people working in the healthcare industry and probably a good behavior for members of the public to adopt for a while.
We have no evidence of people getting infected from packages, however, given that virus can survive on cardboard for up to a day, it is best to take some precautions. When a package arrives, you can use gloves to handle it or wash hands immediately after, and also let it sit for a few days before opening. If you are getting deliveries of food, wash your hands after handling those bags or boxes.
Yes. Coronavirus can be expelled in small droplets that are produced when someone coughs, sneezes, talks or breathes. The risk of transmission is highest though for very close contact (less than 3 feet) but we recommend a distance of 6 feet or 2 arms lengths. There is some evidence from recent studies that virus could remain suspended in the air in droplets for up to three hours. This is another good reason to stay home as much as possible.
During this time, we all want to snuggle with our pets but we want to make sure that it’s safe for us and safe for them. At this time, the CDC reports that there is no evidence that animals play a significant role in spreading the virus that causes COVID-19. We are aware of a small number of pets, including cats and dogs, that have been infected with the virus that causes COVID-19, mostly after close contact with people who had active cases of COVID-19. This means you should treat pets as you would any other family members: Like the rest of the members of your household, you should keep your pets in the house and not transfer them between households. And if someone becomes sick, isolate them from the human and non-human members of the house.
We also know the virus can survive on surfaces and objects, and transmit between people that way. It is technically possible that the virus could survive ON a pet for a short while. There’s no evidence that the virus has ever transmitted between people this way, but to be safe, frequent handwashing and avoiding touching your face will be protective.
If you have a household member with a suspected or confirmed case, act as if it has been confirmed and as if everyone else in the household is infected. Isolate the sick family member. Give them a room that they don’t have to leave, where they can rest. Leave their food by the door, and whatever else they need. Eliminate or reduce the objects coming out of their room and treat those objects as if they are carrying live virus. If you have two bathrooms in the home, use one specifically for the sick individual. Have them monitor and record their symptoms as long as they can, especially their fever. If things worsen or if another household member develops symptoms, contact a health care provider over the phone or online. Since the entire household will have been exposed, everyone needs to stay inside. Have necessary items delivered or make do with what you have in your home. Call your neighbors and lean on your community. And neighbors help each other. It is safe to drop off bags of groceries in front of your neighbor’s house.
The novel Coronavirus is a small sphere with protein spikes on it that allow it to attach to our cells. Below that is an oily layer that coats the virus. When you use detergents like soap or alcohol you disrupt that oily layer and the virus degrades. We also know that on average people touch their faces 23 times an hour! So washing your hands with soap or an alcohol based product will help prevent transmission through that route of infection. It doesn’t mean that you can’t get the virus by other means like inhaling it in droplets or aerosols. We do know from a study done in Hong Kong in the Fall after the SARS outbreak that when the population was being very vigilant with their hygiene that the regular cases of annual flu were substantially reduced. While these data are not specific for Coronavirus they do show that handwashing can reduce the transmission of respiratory transmitted viruses.
In addition to soap and water, alcohol is a recommended cleaning agent to destroy the coronavirus.
Beth told you in a previous video that soap inactivates the coronavirus by destroying the lipid, or fatty, bilayer that holds the virus together. When a virus’ proteins, lipids and RNA fall apart, the components are no longer viable and virus becomes inactive.
That’s how alcohol works, too. When you soak a virus in alcohol – in this case ethanol or isopropanol – and let it air dry, the alcohol breaks down the fatty bilayer that holds the virus together.
Specifically, you’ll find 70% alcohol easily available. Anything between 60-80% alcohol will work just fine. People will sometimes assume that if 70% alcohol is good at destroying viruses, then 90% must be better. This is NOT true. Anything over 80% alcohol will evaporate quickly and may not have enough time to destroy the lipid membrane sufficiently.
Similarly, alcohol that is weaker than 60% will not destroy the virus’s lipid layer, it has too much water in it. This also means you shouldn’t try to use alcohol that is meant for consumption – a standard bottle of vodka is 80 proof, which means it’s only 40% alcohol and will not effectively destroy the virus.
Essential oils also have a limited effective time of action, due to their volatile nature. So while essential oils like tea tree oil are known for having anti-microbial, non-bleaching properties, these anti-microbial properties are significantly weaker than synthetic compounds.
To destroy the coronavirus, soap is most effective at breaking down the fat layer, and 60-80% alcohol cleaners are also highly effective.
Every time you go out to get household necessities, you’re taking on some risk of exposing yourself to the virus or possibly transmitting it to others, if you’re infected and don’t know it. And we all know you have to spend money to buy stuff. In a time of physical distancing and not touching objects other people have just touched, what’s the best way to pay? So handing over a credit card and then getting it back is not ideal. The virus survives reasonably well on plastic and rapid exchanges, like credit card handoffs, are particularly risky. Cash isn’t much better, the rapid exchange means the more rapid decay rate of the virus on paper isn’t really a factor.
Your best options are swiping your credit card yourself and never handing it off or mobile payment with a smartphone where again, you don’t hand anything over and you don’t take anything back. When possible, I prefer to use the self checkout, which protects a potential cashier from me and protects me from them.
It is possible to spread the coronavirus with your shoes. If you’re walking in a common area, particularly indoors, there’s a chance someone sneezed or coughed and gravity sent their respiratory droplets to the floor. If the flooring material is tile, stone, vinyl, or another nonporous material, the virus may survive on it. If you walk through it, you could pick it up on your shoe. If those public floors are cleaned well, the risk is significantly reduced. Proper cleaning means using correctly diluted bleach and letting it sit on the surface for ten minutes before wiping it off. If that wasn’t done, this is still an easily managed problem. When you get home, take your shoes off just inside the door and leave them there. Don’t risk dragging the virus into your house and onto your own floors, especially if you have kids or pets, who might pick it up while crawling or zooming. Stuck to the bottom of your shoe with nowhere to go, the virus will dry out and no longer be viable.
You’ve probably heard that a few tigers and other big cats at the Bronx Zoo developed COVID-19-like symptoms. One was tested and was found to be positive. The others are also presumed infected with SARS-COV-2. An asymptomatically infected zookeeper likely unknowingly transmitted the infection. We don't know whether that person transmitted the virus to each of the infected big cats or if that zookeper transmitted the virus to just to one animal, and then the cats infected each other. The animals are all expected to recover. If now you’re worried about your pets, remember, tigers are not very closely related to domestic animals, even your housecats. There’s still no evidence that house pets can transmit the virus to humans. Of course, if you have COVID-19 or suspect you may have it, avoid contact with people and your pet. In that case, your pet could possibly aid in virus transmission to other household members as a fomite, the same way a doorknob could.
When someone gets infected, how long does it take for them to become infectious? There are two parts to this.
First: The time from infection to symptoms is called the incubation period. Using large data sets from China, a few studies have estimated this time to be about 5.1 or 5.2 days for people who became symptomatic. Recall that some people never become symptomatic, so as with anything, there is a significant amount of individual variation around these numbers, but for simplicity, let’s move forward with the mean values.
For this novel coronavirus, scientists used data from China to estimate that 44% of secondary cases were infected during the presymptomatic phase of primary infection. This tells us that the Latent period is shorter than incubation period for this virus. This study inferred that infectiousness started around 2.3 days before symptom onset and peaked at 0.7 days before symptom onset.
Second: the time from infection to becoming infectious is called the latent period.
If we combine what we learned about the incubation period and asymptomatic transmission from these studies, that would suggest that the latent period, or the amount of time until an infected person becomes infectious is about 3 days.
Some people are worried about the risks associated with ordering takeout. The virus is not transmitted through foods, it’s not a food-borne pathogen like the viruses and bacteria that cause what we often refer to as “food poisoning”. This means that uncooked or cold foods, like salad or sushi, do not pose any additional risk of coronavirus exposure. In general, food prepared in a restaurant kitchen that meets health and safety standards, and there remains open, will be safe. Anything that comes out of a kitchen, including the boxes your food is actually in, should not pose a risk of virus exposure or transmission. The onset of the coronavirus pandemic further prompted additional health and safety measures and chefs and kitchen staff have been wearing masks to prevent the spread of the virus from unknowing asymptomatic infections. The items you should take precautions with include any external packaging that your takeout order may come in. Those bags pass through many hands after they leave the kitchen. For example, if you get your takeout boxes in a plastic bag, toss the bag, wash your hands, and then get into your food. You should also be taking precautions during handoffs, which means delivery or pickups. Any time you’re interacting with someone outside of your household, just keep a safe six foot distance. By taking just a few precautions, you can safely order takeout, help your local restaurants, and enjoy your favorite foods.
We should all be wearing masks when we leave our houses, but are gloves also a necessary precaution for day to day activities? Gloves themselves do not kill the virus. If you’re wearing gloves and you touch something that has virus on it, it can transfer to your gloves. If you then touch your face, you’re just using your gloves to transfer the virus from a source to your face. You can make that mistake with or without gloves on. In some cases, wearing gloves give people a false sense of security, or a sense that they can safely touch things with reduced risk. That will increase a person’s exposure, and in that case gloves are not a good choice. It is more effective to wash your hands frequently and not touch your face than it is to wear gloves and become careless. Wearing gloves does not automatically increase caution or awareness, especially when once the wearer becomes accustomed to them. Gloves are only as effective as handwashing if they’re used properly and disposed of or washed properly. So it’s not necessary for everyone to wear gloves for routine activities.
Several people have emailed with concern about striking the right balance between proper handwashing and hypochondria or anxiety as we return to work. First it is important to remember that most transmission is via respiratory droplets but we do know that good handwashing practice prevents other viruses like the flu. You should always wash your hands after you have been to the bathroom of course and before you eat. How frequently you wash your hands beyond that depends on your circumstance. If you work at your desk all day, you could start by wiping down your desk and keyboard when you arrive. Then you could sanitize your hands before you leave your desk to protect others and again as you return to protect yourself from any surfaces you touched. The great thing about wearing a mask, is that it not only reduces your transmission to others from respiratory droplets, but also keeps you from touching your own face. If you work in high traffic, high risk areas, you might choose to use hand sanitizer every hour or so, or between clients, etc.
For most people, a return to work following quarantine will present an increase in contacts, and therefore an increase in the risk of exposure to COVID-19. For immunocompromised people, we expect that there is an increased risk of becoming infected and experiencing severe symptoms, but we actually don’t have enough data yet to know for certain. However, it is extremely important to reduce risk and avoid infection for people who are immunocompromised. As economies and workplaces resume operations, this means working remotely (or allowing other to work remotely) as much as possible. It is also important to consciously reduce risk of exposure while out: be extra vigilant about masks, social distancing, and hand washing. Close contacts with people outside of the household should be avoided entirely. The CDC defines close contacts are interactions over less than six feet of distance that are over 15 minutes long.
If an immunocompromised individual’s work involves contact with a lot of people – like a restaurant server or bartender, educator, health care worker – it is even more important for them and everyone around them to wear masks and keep the necessary six feet of distance. We must consider the additional possibility that an infected, immunocompromised individual may shed virus for a longer period of time and should be vigilant in protecting themselves as well as everyone around them. Be mindful of yourself and your coworkers, remember that everyone has different health care needs and concerns. Our communities are only as safe as our least cared for members.
As people return to work and spend time in their communities, it is important to discuss the efficacy of different facial coverings. There has also been some misinformation being shared in the media about this lately. Plastic face shields are commonly used by medical personnel as barrier protection against splashes and splatters of respiratory secretions that occur during risky/up close interactions with patients. These same health care personnel also always wear either an N95 respirator or a surgical mask at the same time to prevent inhalation of virus. There is no evidence that face shields, that are open by design, prevent the inhalation or exhalation of viruses. For the average member of the public, who is not exposed to splash or splatter events in the face, a shield is unhelpful. A cloth face covering, instead, is the best option for protection. Cloth masks are best at preventing others from being exposed to virus from the respiratory tract of the wearer. They also provide some protection to the wearer, against larger droplets that may carry virus. So, be kind and wear a mask for others. If we all do this, we will drastically reduce transmission of the virus.
Some recent studies have demonstrated that virus, present in fecal matter, can get sprayed around bathrooms following the flushing of a toilet. What is not clear is whether this virus is ‘infectious’. What that means is whether the virus in the air or on bathroom surfaces would be able to cause disease if it got entry into a person’s respiratory tract. The best advice is to put the toilet seat cover lid down before you flush to limit the spray and protect others who come after you. Also treat all surfaces in bathrooms like they might be contaminated. Wash your hands thoroughly and use a paper towel to open the door handle on the way out. Public bathrooms commonly do not have seat covers, however. Establishments might like to install them and add signage indicating to put them down before flushing. Alternatively, establishments could close alternating stalls to use to provide some physical distance between users. If it is a small bathroom with only a few stalls you could limit occupancy of the bathroom to one person at a time.
We know that good airflow can help reduce the possibility of infection. That is why the risk of transmission is much lower outdoors than indoors. Opening windows and doors will help with airflow and this process can also be assisted with the use of fans. This is not an option in all buildings, however, and in colder regions during winter. Occupants can check with their building facilities staff to make sure the mechanical operations for airflow are functioning and have been effectively restarted/filters cleaned, particularly if they have been shut down. They can also discuss whether it is possible to increase the air turnover rate. This also be more difficult to do in the colder months, however, when rapid air turnover makes the building harder to heat. Building operations staff can consult the CDC website for an official list of these recommendations.
Coronavirus is not a sexually transmitted virus; however, there has been very little research in this area. The virus can be transmitted during sex via inhalation of respiratory droplets and the exchange of saliva during kissing. We also know that virus is present in the feces. The best advice is to avoid having sex with partners that live outside your household or who are not in your quarantine bubble/close contacts. You might consider making the best of technology to have sex safely by phone or virtually. If you do plan to have sex with someone not in your household or close contacts, try to keep the number of partners low, both partners should wear a mask, avoid kissing and oral/anal play, and select positions that have partners facing in opposite directions. If you can, talk about your expectations in advance. Importantly, everyone should avoid having sex if you or your partner has symptoms of COVID-19 or if one of you has recently been exposed to an infected person.
Several months ago, a coalition of scientists urged the WHO to change its messaging to indicate that SARS-CoV-2 could be transmitted by aerosols. Recently, the CDC provided guidance on its website that SARS-CoV-2 might be airborne and then rapidly removed the information. So, what does the evidence say and what does it mean for how to protect yourself? It is generally agreed that like the flu virus, most of SARS-CoV-2 transmission occurs via large droplets that are expelled while talking, breathing, singing, coughing and sneezing. The size of those droplets is such that they fall out of the air rapidly and do not travel very far. This is the basis of the guidance for staying 6 feet apart and wearing masks when you must be closer to people. It also agrees with the data showing that most infections occur between close contacts. There is also evidence, however, that the virus can be expelled in much smaller particles called aerosols that can travel further (some data showing 27 feet) and that can remain in the air for longer periods. Air sampling in hospitals for example has found evidence of virus. The question that remains is whether the virus from these aerosols can infect people. Part of that equation is understanding just how much virus you need to inhale to become infected. We just don’t know. There is also some evidence from studies of infection clusters suggesting airborne transmission. Infections that were tied to a bus in China and a choir in Washington demonstrated that people who became infected were not necessarily sitting near to the infected individual. Additionally, a recent study on an international flight has demonstrated that an infected passenger in business class mostly infected people around him but also people in the economy section. Infection of people in economy could have occurred by aerosols since the sections of the plane do not mix, although contact with the infected individual may also have occurred at check-in or during baggage pickup. There is also an example of infection happening in a restaurant, with exposure likely due to virus dissemination by an air conditioning unit. These studies indicate that aerosol transmission may be possible indoors. As people move into the colder months in the Northern hemisphere, it is important to weigh up the potential risk of aerosol transmission when selecting your indoor activities. The rate of air turnover or ventilation, length of exposure, degree of crowding/ability to keep some distance and whether people are wearing masks should be considered.