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. 2022 Sep;22(9):1313-1320.
doi: 10.1016/S1473-3099(22)00292-4. Epub 2022 Jun 2.

Effectiveness of mRNA vaccine boosters against infection with the SARS-CoV-2 omicron (B.1.1.529) variant in Spain: a nationwide cohort study

Susana Monge  1 , Ayelén Rojas-Benedicto  2 , Carmen Olmedo  3 , Clara Mazagatos  4 , María José Sierra  5 , Aurora Limia  3 , Elisa Martín-Merino  6 , Amparo Larrauri  4 , Miguel A Hernán  7 ; IBERCovid
Collaborators, Affiliations

Effectiveness of mRNA vaccine boosters against infection with the SARS-CoV-2 omicron (B.1.1.529) variant in Spain: a nationwide cohort study

Susana Monge et al. Lancet Infect Dis. 2022 Sep.

Abstract

Background: The omicron (B.1.1.529) variant of SARS-CoV-2 has increased capacity to elude immunity and cause breakthrough infections. The aim of this study was to estimate the effectiveness of mRNA-based vaccine boosters (third dose) against infection with the omicron variant by age, sex, time since complete vaccination, type of primary vaccine, and type of booster.

Methods: In this nationwide cohort study, we linked data from three nationwide population registries in Spain (Vaccination Registry, Laboratory Results Registry, and National Health System registry) to select community-dwelling individuals aged 40 years or older, who completed their primary vaccine schedule at least 3 months before the start of follow-up, and had not tested positive for SARS-CoV-2 since the start of the pandemic. On each day between Jan 3, and Feb 6, 2022, we matched individuals who received 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 risk ratios (RR) and risk differences. Vaccine effectiveness was calculated as one minus RR.

Findings: Between Jan 3, and Feb 6, 2022, 3 111 159 matched pairs were included in our study. Overall, the estimated effectiveness from day 7 to 34 after a booster was 51·3% (95% CI 50·2-52·4). 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 ChAdOx1 nCoV-19 (Oxford-AstraZeneca), 55·3% (52·3-58·2) with mRNA-1273 (Moderna), 49·7% (48·3-51·1) with BNT162b2 (Pfizer-BioNTech), and 48·0% (42·5-53·7) with Ad26.COV2.S (Janssen). Estimated effectiveness was 43·6% (40·0-47·1) when the booster was administered between 151 days and 180 days after complete vaccination and 52·2% (51·0-53·3) if administered more than 180 days after primary scheduled completion.

Interpretation: Booster mRNA vaccine-doses were moderately effective in preventing infection with the omicron variant of SARS-CoV-2 for over a month after administration, which indicates their suitability as a strategy to limit the health effects of COVID-19 in periods of omicron variant domination. Estimated effectiveness was higher for mRNA-1273 compared with BNT162b2 and increased with time between completed primary vaccination and booster.

Funding: None.

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Conflict of interest statement

Declaration of interests We declare no competing interest.

Figures

Figure 1
Figure 1
Study profile
Figure 2
Figure 2
Estimates of SARS-CoV-2 infection risk by booster status and booster vaccine type (A) Pfizer (BNT162b2), (B) Moderna (mRNA-1273), and (C) overall. Shaded areas are 95% CI.
Figure 3
Figure 3
Estimates of SARS-CoV-2 infection risk by booster status and interval since complete vaccination (A) 91–150 days, (B) 151–180 days, and (C) more than 180 days. Shaded areas are 95% CI.
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Comment in

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Supplementary concepts