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The Effectiveness of mRNA Vaccine Boosters for Laboratory-Confirmed COVID-19 During a Period of Predominance of the Omicron Variant of SARS-CoV-2
26 Pages Posted: 15 Feb 2022More...
Background: The effectiveness of mRNA-based boosters against COVID-19 during the Omicron era has not been studied in follow-up studies by age, sex, time since complete vaccination, type of primary vaccine, and type of booster.
Methods: We linked data from nationwide population registries in Spain to select community-dwelling individuals ≥40 years, fully vaccinated ≥3 months ago and without prior SARS-CoV-2 positive tests. On each day between 3 January and 6 February 2022 we matched individuals receiving a booster mRNA vaccine and controls of the same sex, age group, postal code, type of vaccine, time since primary vaccination and number of previous tests. We estimated risk of laboratory-confirmed SARS-CoV-2 infection using the Kaplan-Meier method and compared groups using ratios and differences.
Results: The estimated effectiveness (95% confidence interval) during days 7 to 34 after a booster was 51.3% (50.2, 52.4) overall, higher for females and people aged 60-79. Estimated effectiveness was 52.5% (51.3, 53.7) for an mRNA-1273 booster and 46.2% (43.5, 48.7) for a BNT162b2 booster. Effectiveness was 58.6% (55.5, 61.6) if primary vaccination had been with or ChAdOx1-S, 55.3% (52.3, 58.2) with mRNA-1273, 49.7% (48.3, 51.1) with BNT162b2 and 48.0% (42.5, 53.7) with Ad26.cov2.S. Estimated effectiveness was 43.6% (40.0, 47.1) when the booster was administered 6 months after complete vaccination, and 52.2% (51.0, 53.3) at longer intervals.
Conclusions: Booster mRNA vaccine-doses were moderately effective in preventing SARS-CoV-2 Omicron infection for over a month after administration. Estimated effectiveness was higher for mRNA-1273 compared with BNT162b2 and increased with time since complete vaccination.
Funding Information: None.
Declaration of Interests: Authors declare no support from any organisation for the submitted work; no financial relationships with any organisations that might have an interest in the submitted work in the previous three years, no other relationships or activities that could appear to have influenced the submitted work.
Ethics Approval Statement: This study was approved by the research ethics committee at the Instituto de Salud Carlos III (approval no. CEI PI 98_2020).
Keywords: Covid-19, SARS-CoV-2, Omicron, vaccines, effectiveness, Pfizer, Moderna
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