Browsing by Author "Cuadrado, Cristóbal"

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    Effectiveness of the second COVID-19 booster against Omicron: a large-scale cohort study in Chile
    (2023) Jara Vallejos, Alejandro Antonio; Cuadrado, Cristóbal; Undurraga Fourcade, Eduardo Andrés; García, Christian; Nájera, Manuel; Bertoglia, María Paz; Vergara, Verónica; Fernández, Jorge; García-Escorza, Heriberto; Araos, Rafael
    In light of the ongoing COVID-19 pandemic and the emergence of new SARSCoV-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 nonvaccination, 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 ofimmunity. 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.