BCG vaccination in infancy does not protect against COVID-19. Evidence\n from a natural experiment in Sweden

The Bacille Calmette-Gu\\'erin (BCG) tuberculosis vaccine has immunity\nbenefits against respiratory infections. Accordingly, it has been hypothesized\nthat it may have a protective effect against COVID-19. Recent research found\nthat countries with universal Bacillus Calmette-Gu\\'erin (BCG) childhood\nvaccination policies tend to be less affected by the COVID-19 pandemic.\nHowever, such ecological studies are biased by numerous confounders. Instead,\nthis paper takes advantage of a rare nationwide natural experiment that took\nplace in Sweden in 1975, where discontinuation of newborns BCG vaccination led\nto a dramatic fall of the BCG coverage rate from 92% to 2% , thus allowing us\nto estimate the BCG's effect without all the biases associated with\ncross-country comparisons. Numbers of COVID-19 cases and hospitalizations were\nrecorded for birth cohorts born just before and just after that change,\nrepresenting 1,026,304 and 1,018,544 individuals, respectively. We used\nregression discontinuity to assess the effect of BCG vaccination on Covid-19\nrelated outcomes. This method used on such a large population allows for a high\nprecision that would be hard to achieve using a classical randomized controlled\ntrial. The odds ratio for Covid-19 cases and Covid-19 related hospitalizations\nwere 0.9997 (CI95: [0.8002-1.1992]) and 1.1931 (CI95: [0.7558-1.6304]),\nrespectively. We can thus reject with 95\\% confidence that universal BCG\nvaccination reduces the number of cases by more than 20% and the number of\nhospitalizations by more than 24%. While the effect of a recent vaccination\nmust be evaluated, we provide strong evidence that receiving the BCG vaccine at\nbirth does not have a protective effect against COVID-19.\n