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Short Term Reduction in the Odds of Testing Positive for SARS-CoV-2; a Comparison Between Two Doses and Three doses of the BNT162b2 Vaccine

By Tal Patalon, Sivan Gazit, Virginia E. Pitzer, Ottavia Prunas, Joshua L Warren, Daniel M. Weinberger

Posted 31 Aug 2021
medRxiv DOI: 10.1101/2021.08.29.21262792

With the evidence of waning immunity of the BNT162b2 vaccine, a national third dose vaccination campaign was initiated in Israel during August 2021; other countries have announced their intention to administer a booster shot as well. Leveraging data from Maccabi Healthcare Services, we conducted a preliminary retrospective study aimed at evaluating initial short-term effectiveness of a three dose versus a two dose regimen against infection due to the Delta variant of SARS-CoV-2, using two complementary approaches; a test-negative design and a matched case-control design. We found that 7-13 days after the booster shot there is a 48-68% reduction in the odds of testing positive for SARS-CoV-2 infection and that 14-20 days after the booster the marginal effectiveness increases to 70-84%. Further studies are needed to determine the duration of protection conferred by the third dose and its effect on severe disease.

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