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

Abstract

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.

Effectiveness of a third dose of the BNT162b2 mRNA COVID-19 vaccine for preventing severe outcomes in Israel: an observational study

“…The first study estimated a reduction of 92–97% in the risk for severe disease starting from day 12 after receipt of the third dose, 19 but did not adjust for pre-existing clinical conditions related to the risk of severe disease, and did not evaluate the effectiveness within subgroups. A second study, which adjusted for various confounders and used a test-negative design, estimated a reduction of 70–84% in the probability of testing positive for SARS-CoV-2 among the vaccinated, 20 but did not consider more severe outcomes.…”

Effectiveness of a Third Dose of BNT162b2 mRNA Vaccine

“…In a national study, focusing on the 60-and-over population, with a maximum follow-up period of 31 days, the adjusted VE rate was 89.7% [ 8 ]. Another Israeli HMO study that followed up members aged ≥40 years for a maximum 20-day period also found a reduction in infection rates of between 70% and 84% [ 9 ]. The longer follow-up period in the present study indicates that while the risk of infection increased in the first month of follow-up, rates of infection dropped by the second month.…”

Role of Senescence and Aging in SARS-CoV-2 Infection and COVID-19 Disease

“…Indeed, preliminary findings have shown that a third Pfizer booster shot for those aged above 60 years was able to reduce the risk of infection by 86% and reduced the risk of severe COVID-19 by 92% [ 246 ]. Other studies also show that the third booster shot is capable of inducing vaccine effectiveness increases and restoration of protection in those individuals infected with the Delta variant [ 247 , 248 ]. Many other countries, including Ireland, UK and the USA are now also rolling out mass booster vaccination campaigns.…”