A tuberculosis vaccine may be linked to a lower risk of dying from COVID-19, but researchers caution that it’s not time to stock up on a supply.

In a study published Thursday, researchers found links between populations who had high levels of bacillus Calmette–Guérin (BCG) vaccinations, a common tuberculosis vaccine, and lower levels of COVID-19 mortality. The link provides some early evidence that the BCG vaccination may protect against COVID-19 deaths, according to the peer-reviewed study published in the Proceedings of the National Academy of Sciences.

“The purpose of using the BCG vaccine to protect from severe COVID-19 would be to stimulate a broad, innate, rapid-response immunity,” Luis Escobar, one of the study’s authors and a disease ecologist at the Virginia Tech College of Natural Resources and Environment, told Medical Xpress. The report would seem to challenge the World Health Organization’s position, released in April, that there is “no evidence” that the BCG vaccine protects against COVID-19.

The BCG vaccine was first used on humans in 1921, and became widely used around the world through the 1970s. Many countries in Europe, however, stopped routine inoculation of newborns in the 1970s amid falling levels of tuberculosis infections, according to the study. Escobar and his colleagues examined data from countries with high BCG vaccination rates, such as Brazil and Mexico, with places that have lower rates, like the United States, where the BCG vaccine was never widely used.

After adjusting the data to account for differences such as relative age and the health of various populations, the researchers found that BCG vaccination rates may explain, at least partly, why death rates in countries like Italy, France, and Spain are much higher than in countries like Greece, Hungary, and Poland.

The authors of the study warn that the link they found doesn’t mean that countries should immediately begin stockpiling BCG supplies.

“We’re not looking to advise policy with this paper,” Escobar said, who explained that the purpose of the study was to instead call for more research into the relationship between the BCG vaccine and the COVID-19 pandemic.

In response to a previous study showing similar results in June, researchers at the Center for Economic Policy Research, a think tank based in the U.S., cautioned that a spike in demand for the BCG vaccine could leave millions across the world vulnerable to deadly tuberculosis infections.

“The BCG vaccine is already in low supply,” the researchers wrote. “[It’s] an important tool in the fight against tuberculosis—a lethal disease that killed 1.5 million people in 2018.”

If more research adds evidence to the notion that the BCG vaccine may help protect against the most severe cases of COVID-19, the world may have to ramp up BCG vaccine production rather than divert existing supplies from areas vulnerable to tuberculosis outbreaks.

“Production would have to increase to meet the sudden spike in vaccine demand in order to prevent a delay in distribution to countries that very much need it to fight tuberculosis,” Carolina Barillas-Mury, an author of the study and a disease researcher at the U.S. National Institutes of Health told Medical Xpress.

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