The global health crisis of novel coronavirus pandemic is probably the greatest challenge since the World War II. The pandemic has affected most of the countries, areas or territories. The causative agent for this disease is Severe Acute Respiratory Syndrome-Related Coronavirus- 2 strain (SARS-CoV-2). Researchers all over the world are making huge efforts to develop treatment or vaccine against this novel coronavirus strain. Till date, there is no proper treatment for this COVID-19 pandemic. The only treatments in use are supportive and preventive. Thus, having a strong immune system is what helps a person to get rid of this disease and to survive.
Another fact that griped the attention of researchers is that the impact of the disease is different in different regions or countries. The difference can be because of differences in cultural norms, controlling efforts, and health infrastructure.
What research says!
Study suggests that there may be a possible correlation of Bacillus Calmette-Guérin (BCG) childhood vaccination with lesser mortality rate for COVID-19 pandemic. Countries around the globe have different policies for early childhood BCG vaccination.
The study published in medRxiv Journal suggests that there seems to be a positive correlation of BCG vaccination with reduced mortality rate for COVID-19. The data suggests that mortality and morbidity rates are higher in countries having no particular universal policies of BCG vaccination. These include Italy, Nederland, USA on top of the list. Iran reported massive number of mortality and morbidity due to COVID-19 pandemic. And, Iran is among those courtiers with late start of BCG vaccination policy.
On the other hand, those countries having a distinct policy for BCG vaccination. These countries have shown lesser cases of infection and lesser deaths due to coronavirus. For instance, Japan had reported some of the earliest cases of coronavirus infection but the mortality rates are low despite not having adopted some the more restrictive social isolation measurements. Thus, it can be a great breakthrough in developing a vaccine against novel coronavirus strain if there is a positive association of BCG vaccination and low mortality of COVID-19.
What is BCG vaccine?
BCG is abbreviation of Bacillus Calmette-Guérin vaccine. The vaccine is widely used for newborns to provide immunity against tuberculosis (TB). The vaccine consists of live attenuated strain derived from an isolate of Mycobacterium bovis. Many countries including Japan, china, Pakistan have adopted the universal BCG vaccination policy in newborns. While other countries such as Italy, Spain, France, and Switzerland, have suspended their universal vaccine policies due to comparatively low risk for developing tuberculosis or M. bovis infections.
Study reveals that BCG vaccine induces adaptive immune response. This involves activation of both, CD4+ and CD8+ T cells as well as elevated production of interferon IFN-γ. These enhance the anti-mycobacterial activity of macrophages cells of immune system. Cytokines release also contributes to activate B cells and the ensuing generation of antigen-specific antibodies by plasma cells.
The BCG-specific CD4+ and CD8+ T cells change to a memory phenotype, with functional features of effecter memory T cells which secrete IFN-γ. These memory T cells not only generate a rapid and strong lympho-proliferative response to TB antigens but also effective for several months after vaccination.
Several vaccines including the BCG vaccine generate positive non-specific (heterologous) immune effects. It leads to better immune response against other non-mycobacterial pathogens. For instance, a BCG vaccinated mice infected with the vaccinia virus, were protected by enhanced IFN-Y production from CD4+ cells. This particular phenomenon is named as trained immunity. Moreover, the BCG vaccination appreciably increases the production of pro-inflammatory cytokines, specifically IL-1B, which play a vital role in antiviral immunity.
What if BCG vaccine is effective against COVID-19 disease!
The results from this study suggest possible correlation of BCG vaccine with reduced number of reported cases of novel coronavirus infection. BCG vaccination might provide some protection particularly against novel coronavirus. The research suggests that BCG might confer long-lasting immunity and protection against the present strain of coronavirus.
However, before using this intervention, there is need of more randomized controlled trials. Moreover, the researchers should analyze novel coronavirus strain from different countries and population to determine if the vaccine works for mutant coronavirus strains. And to analyze how fast it induces immune repose against COVID-19. There is no proof that BCG vaccination can work for boosting immunity on elderly and immune-compromised people.
BCG vaccination is generally innocuous and injected through skin. The main side effect is inflammation at the site of injection. On the other hand, BCG is contraindicated in immune -compromised people as well as pregnant women. Thus, there is need of detailed analysis to ensure the safety of this possible intervention against novel coronavirus or COVID-19 pandemic which will surely take sometime.