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.

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 / Mateo-Urdiales, A.; Sacco, C.; Fotakis, E. A.; Del Manso, M.; Bella, A.; Riccardo, F.; Bressi, M.; Rota, M. C.; Petrone, D.; Siddu, A.; Fedele, G.; Stefanelli, P.; Palamara, A. T.; Brusaferro, S.; Rezza, G.; Pezzotti, P.; Fabiani, M.. - In: THE LANCET INFECTIOUS DISEASES. - ISSN 1473-3099. - 23:12(2023), pp. 1349-1359. [10.1016/S1473-3099(23)00374-2]

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

Sacco C.
Secondo
;
Rezza G.;
2023-01-01

Abstract

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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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/20.500.11768/157356
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