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If you are sick with COVID-19 and then you recover, does this mean that you are protected against infecting your partner, your children, your newborn baby? Does it mean that you are protected against becoming ill a second time with the same disease? Along with affecting personal and family decisions of people throughout the world, knowing the answers to these questions would have profound implications on public health measures, hospital procedures, and return-to-work policies. If you are a health worker, for example, and if recovering from COVID-19 makes you immune, you would be protected without the same personal protective measures that others require to avoid getting sick. This would afford you peace of mind, but it would also save an enormous amount of time that you would otherwise need for donning and doffing personal protective equipment.
The central question surrounding COVID-19 immunity is whether infection with SARS-CoV-2 (the virus that causes COVID-19) confers what is called sterilizing immunity in survivors. This is the phenomenon in which the immune system learns to recognize the disease-causing agent, eliminate it from the body, and, if the person is ever exposed to the agent again, be able to eliminate it so quickly and completely that it will not make the person sick, while also neutralizing it so that the person cannot spread it to somebody else. This is the kind of immunity that a person develops from certain diseases for which the earliest vaccines were developed, such as smallpox, measles, rubella, and mumps. Generally, developing such illnesses once confers long-lasting immunity. This is due to characteristics of how the immune system interacts with each particular infectious agent, and those same characteristics make it easier to develop a vaccine that also confers complete, long-lasting immunity. Similarly, if SARS-CoV-2 proves to confer sterilizing immunity, then the chances will be good that the vaccines that are now being developed and tested will work very well, just as the measles-mumps-rubella vaccine works very well. On the other hand, if people are not fully protected after recovering from COVID-19, it will mean either that COVID-19 vaccines will be challenging to develop or that such vaccines will confer only partial protection. The latter type of vaccine would still be extremely useful against the pandemic, but it would go hand in hand with concerns that getting vaccinated or having the disease and recovering would not necessarily prevent you from spreading it to others.
One of the main reasons why infectious disease experts have been concerned that people might be able to become infected a second time with SARS-CoV-2 and that they also might remain infectious for many months after getting sick has to do with test results. As we have discussed here on The Pulse , there are different way to test for SARS-CoV-2 infection.
One way is to swab samples from a person’s nose or throat, or to collect sputum, and test the sample for the presence of genetic material that is particular to the virus. In SARS-CoV-2, the genetic material consists of a molecule called RNA, which is something that all organisms contain, but each molecule of RNA has a particular sequence of building blocks that carries genetic information that can act as a fingerprint. To find out if SARS-CoV-2 RNA sequences are present in samples from a person’s nose, throat, or lower respiratory tract, the samples from the person must first be processed with a procedure called RT-PCR. This procedure transcribes the viral RNA messages into messages in the form of DNA, which is then amplified into many copies so that its sequence can be read.
In a recent study, researchers found that many people who test positive with the RT-PCR test after recovering from COVID-19 do not have viral particles in them. Instead, they only have pieces of viral RNA…rather than full viral particles that are capable of spreading the infection.
Another way to test a person is to take a sample of her blood and look for antibodies that her immune system has made against the SARS-CoV-2 virus, but there are different families of antibodies. When your immune system encounters an infectious agent, the two main families of antibodies that appear in your blood are called IgM and IgG, but when you are first exposed, most of the antibodies against the agent that appear in your blood are IgM antibodies. Thus, if your blood test shows a lot of IgM against SARS-CoV-2 and not much IgG against SARS-CoV2, this suggests that that you have a new infection, as your immune system is in the early stages of fighting the virus. In such a person, we’d expect that her RT-PCR test would come out positive, indicating that the virus is actively reproducing in her cells. As the immune response goes on, however, over the course of months in a person who has recovered, blood tests will still show antibodies against the virus, but now they will be mostly IgG antibodies. Thus, if your antibody tests reveal substantial amounts of IgG antibodies against the virus, and not much IgM, it suggests that you were infected a while ago.
In many cases, people recovering from COVID-19 have continued to test positive in their RT-PCR tests –the tests for the presence of viral RNA– even as they develop IgG antibodies. Researchers have been concerned because if you have viral RNA in your body, this implies that the virus is actively reproducing, despite the IgG antibodies revealing that your immune system has been fighting the virus. This, in turn, has led to doubt that the immune response against this virus is sterilizing,
However, the good news that has come out in recent weeks relates to a study that was conducted by the South Korean Center for Disease and Control. In this study, researchers found that many people who test positive with the RT-PCR test after recovering from COVID-19 do not have viral particles in them. Instead, they only have pieces of viral RNA, remnants of the virus analogous to dead bodies, rather than full viral particles that are capable of spreading the infection.
While the Korean study results do not constitute a full answer to the question of whether the immunity conferred by the virus is sterilizing, the study amounts to a hugely important piece of information that should make us optimistic that further research will reveal that the immune system can protect a person from getting sick a second time and prevent her from spreading the virus to others.
As for what this means until scientists learn more, if you have made a full recovery after suffering from COVID-19, it means a couple of things. First, if you are still testing positive for COVID-19 for weeks or months following your recovery, you should not worry that you might be some kind of Typhoid Mary who will spread the disease to others, because probably you are not. Nevertheless, it also means that you should continue to use reasonable precautions, such as wearing a mask while near your infant and washing your hands before handling him or her.