The cases of COVID-19 infection have been rising fast in India, with over 32,000 new cases reported on the morning of July 16th. So far, scientists have not been able to find a definitive cure for this infectious disease. Meanwhile, many existing medicines and vaccines are being tried and tested against this novel coronavirus. While some scientists tested the effect of the BCG vaccine against the COVID-19 infection, scientists from the Banaras Hindu University, India, examined the effects of trained immunity on COVID-19 infection which was gained after the encounter with TB infection. The study is in the pre-print stage and has not been peer-reviewed yet.
Tall claims about the BCG vaccine against COVID-19 infection
Tuberculosis (TB) is an infectious disease caused by the bacteria Mycobacterium tuberculosis which mostly affects the lungs. A person with TB would present with persistent coughing and sputum for more than three weeks. The tuberculosis vaccine Bacillus Calmette Guérin (BCG) is given intradermally, that is through the skin to infants (before attaining the age of 1 year) and adults.
After the COVID-19 pandemic began, some scientists tested the BCG vaccine on COVID-19 patients and claimed that it could not only prevent the spread of infection but also reduce the chances of COVID-19 related deaths.
However, even the large scale studies such as the Diamond Princess cruise study (where the COVID-19 infected people on the cruise were studied for the effects of BCG) showed no significant difference in the infection and death rate after the BCG vaccination.
While TB is an active disease, scientists tested the people with latent TB. In latent TB, the person does not experience any symptoms and cannot spread the disease to others, but they do have the TB bacteria in their body. The bacteria is in the dormant state but can get active to develop TB. In such situations, these people develop trained immunity in their body. Trained immunity is the long-term hyperactivation of in-built (innate) immunity of the body after exposure to a certain disease.
The study: Trained immunity against COVID-19 infection
In this study, scientists collected the data of more than 1.4 million COVID-19 patients from twenty European countries with a prevalence of latent TB infection. These people did not get the mandatory BCG vaccine. The data was published by the Institute for Health Metrics and Evaluation of the University of Washington.
The scientists then examined the health status of these people at three time-points of the ongoing pandemic - on 8th April 2020, 12th May 2020 and 26th May 2020. The scientists examined any correlation of COVID-19 cases and deaths in these patients irrespective of their sex, age, or ethnicity.
Conclusion: The inverse relation of COVID-19 with latent TB infection
The study showed that trained immunity had an inverse relation with COVID-19 infection. The results of the study pointed out that people with latent TB were the least infected amongst the one million people tested. However, latent TB or trained immunity had no significant difference in the death rate of COVID-19 infected people.
The scientists stated in the study that further clinical trials are needed to be done to find out the effect of BCG vaccine on trained immunity.
For more information, read our article on TB and COVID-19.
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