In a letter published in The Lancet on April 30, World Health Organization (WHO) Director-General Tedros A Ghebreyesus and others highlight a few critical issues over the use of BCG vaccine for COVID-19. They underscore the importance of randomised controlled trials of the vaccine to understand its safety and efficacy before using it on healthcare workers.
Randomised controlled trials using BCG vaccine are under way in the Netherlands and Australia to find out whether the vaccine can reduce the incidence and severity of COVID-19 among healthcare workers.
The authors do state that the BCG vaccine, which “enhances the innate immune response to subsequent infections, might reduce viral load after SARS-COV-2 exposure, with a consequent less severe COVID-19 and more rapid recovery”.
A study, posted on March 28 in a preprint server medRxiv, found an association between countries that have a universal BCG vaccination and reduced coronavirus cases — and even deaths. Preprints are yet to be peer-reviewed and published in scientific journals.
The authors cite five reasons countries should wait for the results of the BCG vaccine randomised controlled trials. According to them, the association of fewer COVID-19 cases in countries that have a universal BCG vaccination programme is based on population rather than individual data. Second, the beneficial effects of the BCG vaccine given at birth are “unlikely” to reduce the severity of COVID-19 decades later. “One reason for this is that the beneficial off-target effects of the BCG vaccine might be altered by subsequent administration of a different vaccine,” they write.
Third, there is a possibility, even if remote, that the BCG vaccine ramps up the immune system leading to exacerbation of COVID-19 in a small population of patients with a severe disease. It is already known that the virus induces cytokine storm in some patients, leading to further complications — and even death. Fourth, if not effective against the novel coronavirus, BCG vaccination is likely to give a false sense of security to people, especially during the pandemic. And finally, using the vaccine without evidence of its benefits could further jeopardise vaccine supply, which is already short, to protect children against disseminated TB in high-risk countries.
“BCG given early in life does improve the immune system. The vaccine can prevent intracellular infections. So the protective effect of BCG against COVID-19 is a biologically plausible hypothesis,” Prof. Gagandeep Kang, executive director of the Translational Health Science and Technology Institute (THSTI), Faridabad, had earlier told The Hindu .