Effectiveness of the second COVID-19 booster against Omicron: a large-scale cohort study in Chile

Alejandro Jara, Cristobal Cuadrado, Eduardo A. Undurraga, Christian García, Manuel Nájera, María Paz Bertoglia, Verónica Vergara, Jorge Fernández, Heriberto García-Escorza and Rafael Araos ()
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Alejandro Jara: Pontificia Universidad Católica de Chile
Cristobal Cuadrado: Ministerio de Salud de Chile
Eduardo A. Undurraga: Pontificia Universidad Católica de Chile
Christian García: Ministerio de Salud de Chile
Manuel Nájera: Ministerio de Salud de Chile
María Paz Bertoglia: Ministerio de Salud de Chile
Verónica Vergara: Ministerio de Salud de Chile
Jorge Fernández: Ministerio de Salud de Chile
Heriberto García-Escorza: Ministerio de Salud de Chile
Rafael Araos: Multidisciplinary Initiative for Collaborative Research in Bacterial Resistance (MICROB-R)

Nature Communications, 2023, vol. 14, issue 1, 1-7

Abstract: Abstract In light of the ongoing COVID-19 pandemic and the emergence of new SARS-CoV-2 variants, understanding the effectiveness of various booster vaccination regimens is pivotal. In Chile, using a prospective national cohort of 3.75 million individuals aged 20 or older, we evaluate the effectiveness against COVID-19-related intensive care unit (ICU) admissions and death of mRNA-based second vaccine boosters for four different three-dose background regimes: BNT162b2 primary series followed by a homologous booster, and CoronaVac primary series followed by an mRNA booster, a homologous booster, and a ChAdOx-1 booster. We estimate the vaccine effectiveness weekly from February 14 to August 15, 2022, by determining hazard ratios of immunization over non-vaccination, accounting for relevant confounders. The overall adjusted effectiveness of a second mRNA booster shot is 88.2% (95%CI, 86.2–89.9) against ICU admissions and 90.5% (95%CI 89.4–91.4) against death. Vaccine effectiveness shows a mild decrease for all regimens and outcomes, probably linked to the introduction of BA.4 and BA.5 Omicron sub-lineages and the waning of immunity. Based on our findings, individuals might not need additional boosters for at least 6 months after receiving a second mRNA booster shot in this setting.

Date: 2023
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DOI: 10.1038/s41467-023-41942-y

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