Why a century-old vaccine offers new hope against pathogens

In the early days of the COVID-19 pandemic, when prevention seemed light years away, several scientists launched trials to see whether a tuberculosis vaccine developed in the early 1900s might protect people by bolstering the immune system.

The Bacillus-Calmette-Guerin vaccine has long been known to have broad effects on the immune system, and is still given to infants in the developing world and in countries where TB is prevalent.