Efficacy of monovalent COVID-19 booster began waning by 3 or 4 monthsSouth African researchers report waning monovalent (single-strain) COVID-19 vaccine booster effectiveness against the Omicron subvariants, with estimated efficacy falling to 50% against the BA.1/BA.2 and 47% against BA.4/BA.5 as early as 3 or 4 months after vaccination.In the study, published yesterday in the New England Journal of Medicine (NEJM), the research team estimated the effectiveness of two and three doses of the monovalent Pfizer/BioNTech vaccine against COVID-19 hospitalization among 32,883 patients hospitalized for any cause and tested for COVID-19 from Nov 15, 2021, to Jun 24, 2022.They used a test-negative design to estimate the odds of vaccination among patients who tested positive for COVID-19.The study was conducted before the Aug 31 US Food and Drug Administration (FDA) authorization of the updated bivalent (two-strain) boosters designed to protect against BA.4/BA.5, in addition to the wild-type virus (BA.4/BA.5 has superseded BA.1/BA.2).
The new Pfizer booster is authorized for ages 12 and older, while the Moderna booster is authorized only for adults. The older booster is no longer in use.From Nov 15, 2021, to Feb 28, 2022 (BA.1/BA.2-dominant period) and Apr 15 to Jun 24, 2022 (BA.4/BA.5-dominant period), 18% of patients tested positive for COVID-19.
During both periods, two-dose effectiveness against hospitalization began waning as early as 3 or 4 months after vaccination.Estimated vaccine effectiveness was 56.3% (95% confidence interval [CI], 51.6% to 60.5%) during BA.1/BA.2 dominance and 47.4% (95% CI, 19.9% to 65.5%) amid BA.4/BA.5.