Effectiveness of Inactivated COVID-19 Vaccination Against COVID-19–Related Hospitalization and Severe Outcomes in Adults ≥80 Years During Omicron Circulation in Beijing, China: Retrospective Cohort Study

Background: A large wave of COVID-19 caused by SARS-CoV-2 Omicron subvariants began in Beijing in early December 2022. Objective: This study aimed to evaluate the COVID-19 vaccine effectiveness (VE) in mitigating the risk of COVID-19-related hospitalization during the epidemic. Methods: We conducted a retrospective cohort study linking regional health care data and vaccination registry routinely collected in Beijing. All electronic medical records on COVID-19-related hospital discharges of older inpatients aged ≥80 years during November 2022 and February 2023 were included. Poisson regressions were used to estimate incidence risk ratio of COVID-19-related hospitalization, severe or critical cases, and in-hospital death compared with unvaccinated groups, adjusting for gender and age. VE was calculated as 1 minus incidence risk ratio×100%. Results: A total of 53,789 individuals aged ≥80 years were included, 28,423 (52.84%) were male, 45,270 (84.16%) were aged 80-89 years, and 8519 (15.84%) were aged ≥90 years. Overall, 30,531 (56.76%) were in the vaccine group, with 4524 (8.41%) of the total participants receiving partial vaccination, 20.91% completing the primary series, and 14,761 (27.44%) receiving one booster. Additionally, 23,258 (43.24%) were in the unvaccinated group. Of the 53,789 hospitalized individuals, 17,916 (33.31%) had a COVID-19 diagnosis, 3535 (6.57%) had COVID-19-related hospitalization, 961 (1.79%) were COVID-19 severe or critical cases, and 4130 (7.68%) had in-hospital death. The analysis revealed that the VE of booster vaccination in preventing COVID-19-related hospital, severe or critical COVID-19, and in-hospital death was 63.5% (95% CI 59.8%-66.9%), 66.9% (95% CI 60.1%-72.6%) and 79.4% (95% CI 77%-81.5%), the VE of primary series 56% (95% CI 51.4%-60.2%), 66.8% (95% CI 59%-73%) and 66.4% (95% CI 63%-69.5%). Conclusions: The first booster vaccination was associated with significantly reduced the risk of COVID-19-related severe outcomes in older inpatients aged ≥80 years during the Omicron-dominant period. Considering the potential selection bias and unmeasured confounders, these estimates may reflect both the VE and the better baseline health status of the vaccinated older individuals.