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The Spread of COVID-19 and the BCG Vaccine: Evidence from a Natural Experiment in Germany
17 Pages Posted: 3 Oct 2020More...
Background: Since 1 October 2019, COVID-19 has resulted in nearly 18 million reported cases and 700,000 deaths worldwide. The hypothesis that the Bacillus Calmette-Guérin (BCG) vaccine may offer protection against COVID-19 has motivated clinical trials in Australia, the Netherlands and other countries. The results of these trials will not be known for months.
Methods: We use a regression discontinuity differences-in-differences (RD-DD) design in Germany exploiting differential BCG vaccination practices in the East and in the West during 1945-90. Our analysis compares cases per capita in German counties within 100 km of the former border for cohorts born around 1990, when mandatory vaccination ended in the East and the West continued to not recommended BCG vaccination.
Findings: We analyzed 154,175 COVID-19 cases by single ages reported in 400 counties in Germany on April 24, 2020. We find that cohorts born shortly before and after the policy change exhibit no significant differences in COVID-19 prevalence to those in the west. Eastern counties report fewer log cases per capita than counties just in the west (estimate -.830, 95% CI: -0.528 to -1.132). However, this difference is larger for cohorts born ten years after the policy change (estimate -1.190, 95% CI: -2.384 to 0.003) than those born ten years prior (estimate -0.595, 95% CI: -0.995 to -0.195). A spatial SIR model with commuter flows between German counties produces a differential of -0.588 (95% CI: -1.048 to -0.127) without reference to the BCG vaccine.
Interpretation: We interpret our results as providing evidence against the BCG hypothesis. Instead, our evidence is consistent with discontinuities in commuter flows across the former East Germany border being an important contributor to the discontinuity in COVID-19 cases.
Funding Statement: None.
Declaration of Interests: The authors declare no competing interests.
Keywords: Covid-19, BCG vaccine, trained immunity, Germany, regression discontinuity design, SIR model with commuter flows
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