Clinical Features and Outcomes of Hospitalized Adult Patients With Breakthrough COVID-19 Infections: A Propensity-Score-Matched Observational Study.

In this study, we aimed to evaluate the impact of vaccination on intensive care unit (ICU) admission and in-hospital mortality among breakthrough coronavirus disease 2019 (COVID-19) infections. A total of 3,351 adult patients hospitalized with COVID-19 in the Memorial Healthcare System (Hollywood, Florida) between June 1 and September 20, 2021, were included; 284 (8.5%) were fully vaccinated. A propensity-score-matched analysis was conducted to compare fully vaccinated patients with unvaccinated controls. Propensity scores were calculated on the basis of variables associated with vaccination status. A 1:1 matching ratio was applied using logistic regression models, ensuring balanced characteristics between the two groups. The matched samples were then subjected to multivariate analysis. Among breakthrough infections, vaccinated patients demonstrated lower incidences of ICU admission (10.3% vs. 16.4%; P = 0.042) and death (12.2% vs. 18.7%; P = 0.041) than the matched controls. Risk-adjusted multivariate analysis demonstrated a significant inverse association between vaccination and ICU admission (odds ratio = 0.52, 95% confidence interval: 0.31, 0.89; P = 0.019) as well as in-hospital mortality (odds ratio = 0.57, 95% confidence interval: 0.34, 0.94; P = 0.027). Vaccinated individuals experiencing breakthrough infections had significantly lower risks of ICU admission and in-hospital mortality. These findings highlight the benefits of COVID-19 vaccines in reducing severe outcomes among patients with breakthrough infections.