A new study found evidence that a vaccine used against tuberculosis may help reduce the death rate for COVID-19.
The vaccine, called bacillus Calmette−Guérin (BCG), likely provides nonspecific immunity, meaning protection against other diseases, although the mechanisms are still unclear, the researchers said.
They found through statistical analysis that countries where BCG is widely administered have a lower COVID-19 mortality rate when other factors are accounted for.
A 10 percent increase in the BCG index, which estimates the degree of vaccination in the country, was correlated with a 10.4% reduction in mortality from the coronavirus.
The paper emphasized that further research is needed and the results “should be considered with caution.” Vaccination trials will be needed to corroborate the findings, the researchers wrote. The World Health Organization has cautioned against using the vaccine for COVID-19 without further research.
Clinical trials are being conducted in the Netherlands and Australia.
The findings were published on Thursday in the peer-reviewed US science journal PNAS. The team was headed by Luis Escobar of Virginia Polytechnic Institute, alongside Alvaro Molina-Cruz and Carolina Barillas-Mury.
BCG has been used for over 90 years and some countries conduct national vaccination programs of infants to prevent tuberculosis. It is proven to be safe for children and adults, but its effectiveness in adults is in dispute, as is its safety for the elderly.
The researchers used global data to correlate national BCG vaccination programs to COVID-19 deaths, and attempted to control for confounds, including urbanization, population density, age classes, health care, income and education.
They looked at deaths because fatalities are seen as a more reliable indicator of the extent of coronavirus than confirmed infections.
“Countries with a stronger BCG vaccination policy had significantly lower COVID-19 deaths/million… More broadly, countries with current BCG vaccination had lower deaths as compared to countries with lack of, or interrupted, BCG vaccination,” they wrote.
For example, US states, which do not have BCG vaccination programs, had higher mortality rates than states in Mexico and Brazil, which do have programs, when other variables were controlled. This was true even though the Latin American states, which included Rio de Janeiro, Sao Paolo and Mexico City, were much more dense than the US states.
The researchers wrote that, since most Asian countries have universal BCG vaccination programs, and the US does not, “it is possible that some of the social distancing roll-back strategies taken by Asian countries, in order to restart their economies, may not be effective in North America and western European countries, and could result in a second wave of infections.”
They also compared similar European areas, such as western Germany and eastern Germany, which had different vaccination policies prior to their unification.
In western Germany, where today’s elderly were not vaccinated, the death rate was 2.9 times higher than in eastern Germany, where the elderly were vaccinated as children. Almost all of Germany’s COVID-19 deaths are among individuals over 60.
Western Europe overall has an average mortality rate 9.92 times higher than Eastern Europe, where the vaccine is much more widespread.
France, Germany and Spain previously had BCG programs but stopped them as the disease, which is bacterial, became less prevalent. Other countries, including Russia, Ukraine and China, continued to administer the vaccine. The US never conducted a national BCG program.
Evidence of more broad protection provided by BCG stretches back to the 1920s, the researchers wrote.
Previous publications suggested BCG could help fight COVID-19 but were not accompanied by thorough statistical analysis.
The data covered coronavirus-related deaths through late April.