Anthony King in The Scientist:
One of the oldest vaccines could protect us against our newest infectious disease, COVID-19. The vaccine has been given to babies to protect them against tuberculosis for almost a century, but has been shown to shield them from other infections too, prompting scientists to investigate whether it can protect against the coronavirus. This Bacille Calmette-Guérin (BCG) vaccine, named after two French microbiologists, consists of a live weakened strain of Mycobacterium bovis, a cousin of M. tuberculosis, the bacterium that causes tuberculosis. BCG has been given to more than 4 billion individuals, making it the most widely administered vaccine globally. Because BCG protects babies against some viral infections in addition to TB, researchers decided to compare data from countries with and without mandatory BCG vaccination to see if immunization policies are linked to the number or severity of COVID-19 infections. A handful of preprint publications in the last two months noted that countries with an ongoing BCG vaccination program are experiencing lower death rates from COVID-19 than those without.
One study, for instance, found that mandatory BCG was associated with a significantly slower climb in both confirmed cases and deaths during the first 30-day period of an outbreak. Another modeled mortality in two dozen countries and reported that those without universal BCG vaccination, such as Italy, the US, and the Netherlands, were more severely affected by the pandemic than those with universal vaccination.