Amid ongoing research on the use of the tuberculosis vaccine Bacille Calmette-Guérin (BCG) for controlling COVID-19, experts say the evidence is inconclusive.
Randomised controlled trials are under way in the Netherlands and Australia, and until these are complete, the World Health Organization’s recommendation--to use the BCG vaccine only in trials--should be followed, a new article in The Lancet has said.
Evidence suggests that the off-target effects of the vaccine reduce the severity of COVID-19 infection. Diverting the BCG vaccine--which prevents severe forms of tuberculosis among children--for COVID-19 would decrease its availability for newborns and lead to an increase in disease and deaths from tuberculosis, a scientific brief by the World Health Organisation released on April 12, 2020, had noted.
The Lancet article lists four reasons to avoid such use:
- The BCG vaccine is in short supply, and “indiscriminate use could jeopardise the supply needed to protect children against tuberculosis in high-risk areas”.
- The correlation between countries with routine BCG immunisation and fewer COVID-19 cases is weak because it is unlikely that a childhood vaccine will work after decades, and subsequent vaccines might alter the effects of previous vaccines. Also, the number of reported cases might be influenced by the rate of testing.
- If the BCG vaccine is found to be ineffective against COVID-19, it could “engender a false sense of security”.
- Even in randomised trials, careful monitoring is done to ensure that the increased immune function due to the BCG vaccine does not exacerbate COVID-19 in patients with severe disease.
Major developments around the effects of BCG vaccine
Randomised control trials have shown that certain properties of the BCG vaccine might help with respiratory infections, the article has noted. The BCG-Danish vaccine was found to reduce respiratory tract infections by 73% among adolescents in South Africa.
The vaccine also reduced the yellow fever vaccine viraemia (spread of virus in the blood) by 71% in volunteers in the Netherlands, and the severity of mengovirus in mice in two studies (here and here), the article said. Both these viruses have a single-strand positive-sense RNA virus as SARS-CoV-2 (the COVID-19 virus) does.
There is no evidence that the BCG vaccine can protect people against infection with the SARS CoV-2 virus, WHO’s brief on April 12, 2020 said, adding that the non-specific effects of the vaccine on the immune system “have not been well characterized and their clinical relevance is unknown”.
Two randomised controlled trials are under way, as we said, in the Netherlands and Australia to assess if the BCG vaccine would work against COVID-19, and study if the BCG-Danish vaccine reduces the incidence and severity of COVID-19 in healthcare workers, and the effect this has on time away from work, the Lancet article said.
If the BCG vaccine is able to provide non-specific protection against COVID-19, until a disease-specific vaccine is developed, this would be useful not only for the current pandemic but also for similar outbreaks in the future, said the article.
(Tiwari is a principal correspondent with IndiaSpend.)