Relative effectiveness of monovalent and bivalent mRNA boosters in preventing severe COVID-19 due to omicron BA.5 infection up to 4 months post-administration in people aged 60 years or older in Italy: a retrospective matched cohort study - 23/11/23
, Chiara Sacco, PhD a, b, Emmanouil Alexandros Fotakis, PhD a, b, Martina Del Manso, DSTAT a, Antonino Bella, DSTAT a, Flavia Riccardo, PhD a, Marco Bressi, Meng a, Maria Cristina Rota, MD a, Daniele Petrone, DSTAT a, c, Andrea Siddu, MD d, Giorgio Fedele, PhD a, Paola Stefanelli, PhD a, Anna Teresa Palamara, MD a, Silvio Brusaferro, MD e, Giovanni Rezza, MD d, Patrizio Pezzotti, DSTAT a, Massimo Fabiani, DSTAT a
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Summary |
Background |
Limited evidence is available on the additional protection conferred by second mRNA vaccine boosters against severe COVID-19 caused by omicron BA.5 infection, and whether the adapted bivalent boosters provide additional protection compared with the monovalent ones. In this study, we aimed to estimate the relative effectiveness of a second booster with monovalent or bivalent mRNA vaccines against severe COVID-19 in Italy.
Methods |
Linking data from the Italian vaccination registry and the SARS-CoV-2 surveillance system, between Sept 12, 2022, and Jan 7, 2023, we matched 1:1 each person aged 60 years or older receiving a second booster with a person who had received the first booster only at least 120 days earlier. We used hazard ratios, estimated through Cox proportional hazard models, to compare the hazard of severe COVID-19 between the first booster group and each type of second booster (monovalent mRNA vaccine targeting the original strain of SARS-CoV-2, bivalent mRNA vaccine targeting the original strain plus omicron BA.1 [bivalent original/BA.1], and bivalent mRNA vaccine targeting the original strain plus omicron BA.4 and BA.5 [bivalent original/BA.4-5]). Relative vaccine effectiveness (rVE) was calculated as (1–hazard ratio) × 100.
Findings |
We analysed a total of 2 129 559 matched pairs. The estimated rVE against severe COVID-19 with the bivalent original/BA.4-5 booster was 50·6% (95% CI 46·0–54·8) in the overall time interval 14–118 days post-administration. Overall, rVE was 49·3% (43·6–54·4) for the bivalent original/BA.1 booster and 26·9% (11·8–39·3) for the monovalent booster. For the bivalent original/BA.4-5 booster, we did not observe relevant differences in rVE between the 60–79-year age group (overall, 53·6%; 46·8–59·5) and those aged 80 years or older (overall, 48·3%; 41·9–54·0).
Interpretation |
These findings suggest that a second booster with mRNA vaccines provides additional protection against severe COVID-19 due to omicron BA.5 (the predominant circulating subvariant in Italy during the study period) in people aged 60 years or older. Although rVE decreased over time, a second booster with the original/BA.4-5 mRNA vaccine, currently the most used in Italy, was found to be still providing protection 4 months post-administration.
Funding |
NextGenerationEU-MUR-PNRR Extended Partnership initiative on Emerging Infectious Diseases (project number PE00000007, INF-ACT).
Translation |
For the Italian translation of the abstract see Supplementary Materials section.
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Vol 23 - N° 12
P. 1349-1359 - décembre 2023 Retour au numéro
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