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The Bacille Calmette-Gu\'erin (BCG) tuberculosis vaccine has immunitybenefits against respiratory infections. Accordingly, it has been hypothesizedthat it may have a protective effect against COVID-19. Recent research foundthat countries with universal Bacillus Calmette-Gu\'erin (BCG) childhoodvaccination policies tend to be less affected by the COVID-19 pandemic.However, such ecological studies are biased by numerous confounders. Instead,this paper takes advantage of a rare nationwide natural experiment that tookplace in Sweden in 1975, where discontinuation of newborns BCG vaccination ledto a dramatic fall of the BCG coverage rate from 92% to 2% , thus allowing usto estimate the BCG's effect without all the biases associated withcross-country comparisons. Numbers of COVID-19 cases and hospitalizations wererecorded for birth cohorts born just before and just after that change,representing 1,026,304 and 1,018,544 individuals, respectively. We usedregression discontinuity to assess the effect of BCG vaccination on Covid-19related outcomes. This method used on such a large population allows for a highprecision that would be hard to achieve using a classical randomized controlledtrial. The odds ratio for Covid-19 cases and Covid-19 related hospitalizationswere 0.9997 (CI95: [0.8002-1.1992]) and 1.1931 (CI95: [0.7558-1.6304]),respectively. We can thus reject with 95\% confidence that universal BCGvaccination reduces the number of cases by more than 20% and the number ofhospitalizations by more than 24%. While the effect of a recent vaccinationmust be evaluated, we provide strong evidence that receiving the BCG vaccine atbirth does not have a protective effect against COVID-19.

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