Effectiveness of bivalent mRNA vaccines against medically attended symptomatic SARS-CoV-2 infection and COVID-19-related hospital admission among SARS-CoV-2-naive and previously infected individuals: a retrospective cohort study - 23/11/23
, Calvin J Chiew, MPH a, b, Deanette Pang, BSS a, Vernon J Lee, PhD a, c, Benjamin Ong, MBBS a, d, Lin-Fa Wang, PhD e, Ee Chee Ren, PhD d, f, David Chien Lye, MBBS b, d, g, h, Kelvin Bryan Tan, PhD a, c
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Summary |
Background |
Emergence of the SARS-CoV-2 omicron (B.1.1.529) variant with high immune evasion has led to the development and roll-out of bivalent mRNA vaccines targeting original and omicron strains. However, real-world observational data on effectiveness of bivalent vaccines are scarce. We aimed to assess the relative effectiveness of a fourth vaccine dose with the BA.1-adapted or BA.4/BA.5-adapted bivalent vaccines against medically attended symptomatic SARS-CoV-2 infection and COVID-19-related hospital admission among SARS-CoV-2-naive and previously infected individuals in Singapore.
Methods |
We conducted a retrospective cohort study among Singapore residents aged 18 years and older who had received three monovalent mRNA vaccine doses and were eligible for a fourth dose. Data were collected from official databases on COVID-19 cases and vaccinations maintained by the Singapore Ministry of Health. We analysed the incidence of medically attended symptomatic SARS-CoV-2 infection and COVID-19-related hospital admission between Oct 14, 2022, and Jan 31, 2023, by previous infection status and type of fourth vaccine dose received. Inverse probability-weighted Cox regressions were used to estimate hazard ratios (HRs).
Findings |
2 749 819 individuals were included in the analysis. For the SARS-CoV-2-naive group, a fourth monovalent vaccine dose did not confer additional protection over three monovalent doses against symptomatic infection (HR 1·09 [95% CI 1·07–1·11]), whereas the bivalent vaccine did provide additional protection (0·18 [0·17–0·19]). Among individuals with previous infection, the HR was 0·87 (95% CI 0·84–0·91) and 0·14 (0·13–0·15) with receipt of the fourth monovalent and bivalent doses, respectively. Against COVID-19-related hospital admission, the bivalent vaccine (HR 0·12 [95% CI 0·08–0·18] in SARS-CoV-2-naive participants and 0·04 [0·01–0·15] in previously infected participants) conferred greater benefit compared with the fourth monovalent dose (0·84 [0·77–0·91] in SARS-CoV-2-naive participants and 0·85 [0·69–1·04] in previously infected participants).
Interpretation |
A fourth dose with the bivalent vaccine was substantially more effective against medically attended symptomatic SARS-CoV-2 infection and COVID-19-related hospital admission than four monovalent doses among both SARS-CoV-2-naive and previously infected individuals. Boosters with the bivalent vaccine might be preferred in this omicron-predominant pandemic, regardless of previous infection history.
Funding |
None.
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Vol 23 - N° 12
P. 1343-1348 - décembre 2023 Retour au numéro
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