LITERATURE IS FILLING WITH CONFLICTING STUDIES

But cross-country comparisons showing that some nations with different BCG use had fewer cases of Covid-19 are far from conclusive. Many other factors, such as differences in testing and health care systems — and even migration of people between countries with different BCG vaccine policies — could account for some of the differences. Brazil has a raging outbreak despite broadly using the BCG vaccine. The scientific literature is filling with conflicting studies, with titles that show the lack of consensus: “A shred of evidence that BCG vaccine may protect against Covid-19 and “BCG protects against Covid-19? A word of caution.”

A large study of deaths in Israel cast doubt.

“The BCG vaccine was routinely administered to all newborns in Israel as part of the national immunisation programme between 1955 and 1982,” the study said. “Since 1982, the vaccine has been administered only to immigrants from countries with high prevalence of tuberculosis.” The result? No significant difference between those who received the vaccine and those who didn’t.

“Facts have a nasty habit of overturning circumstantial evidence,” Raza said, adding that the “only way to prove it is through future prospective trials.”

Konstantin Chumakov, associate director of research at the Food and Drug Administration’s Office of Vaccine Research, said when he was growing up in the Soviet Union, his parents — vaccine researchers who studied the off-target effects of the oral polio vaccine in the 1960s and 1970s — gave him the oral polio vaccine every fall before the influenza season because of evidence it provided broad protection.