A retrospective, observational study found that individuals who obtained the tuberculosis-preventing Bacillus Calmette-Guérin (BCG) vaccine were less likely to report symptoms of COVID-19 and less likely to have antibodies in their blood to the infection. This tuberculosis vaccine primes the “innate” immune system, the first line of protection of the body against viruses and other invading species, scientists say. Innate immunity seldom attacks new pathogens that the body has experienced in the past, unlike adaptive immunity. Also, the results of many studies indicate lower rates of infection and mortality in countries with universal neonatal Bacille Calmette-Guérin (BCG) tuberculosis vaccination comparing the impact of coronavirus disease 2019 (COVID-19) worldwide relative to countries without this procedure.

Researchers tested the blood of more than 6,000 healthcare staff in the Cedars-Sinai Health System for signs of antibodies to SARS-CoV-2, the virus that causes COVID-19, in a new study published online on Nov. 19 in The Journal of Clinical Investigation, and also asked them about their medical and vaccine records. They found that workers who had received BCG vaccines in the past—nearly 30 percent of those studied—were substantially less likely to test positive for SARS-CoV-2 antibodies in their blood or to report having had infections with coronavirus or coronavirus-associated symptoms over the prior six months than those who had not received BCG. These results were not linked to whether workers received vaccines against meningococcal, pneumococcal, or influenza.

When scientists evaluated the immune systems of individuals who had the BCG vaccine with those who did not, they found that the immune cells of BCG vaccinated individuals who first responded to the disease were more alert and ready to respond to a possible threat. An alert immune system means that the body is better equipped to combat disease. Studies carried out on babies born in Guinea-Bissau have backed this theory. They proposed that by preventing TB alone, the vaccine could help reduce infant mortality beyond what you might expect.