Vaccination reduces need for emergency care in breakthrough COVID-19 infections: A multicenter cohort study

Bahl, A.; Johnson, S.; Maine, G.; Hernandez Garcia, M.; Nimmagadda, S.; Qu, L.; Chen, N.-W.

Importance: While recent literature has shown the efficacy of the COVID-19 vaccine in preventing infection, its impact on need for emergency care/hospitalization in breakthrough infections remain unclear, particularly in regions with a high rate of variant viral strains. Objective: We aimed to determine if vaccination reduces hospital visits and severe disease in breakthrough COVID-19 infections. Design: Multicenter observational cohort analysis Setting: Eight-hospital acute care regional health system in Michigan, USA Participants: Consecutive adult patients with COVID-19 requiring emergency care (EC)/hospitalization were eligible participants. Between December 15, 2020 and April 30, 2021, 11,834 EC encounters with COVID-19 infection were included. Exposures: COVID-19 vaccination Main Outcomes and Measures: Primary endpoint was rate of COVID-19 emergency care/hospitalization encounters comparing unvaccinated (UV), partially vaccinated (PV), and fully vaccinated (FV) cases. Secondary outcome was severe disease represented as a composite outcome (ICU admission, mechanical ventilation, or in-hospital death). Demographic and clinical variables were obtained from the electronic record. Vaccination data was obtained from the Michigan Care Improvement Registry and the Centers for Disease Control vaccine tracker. Results: 10,880 (91.9%) UV, 825 (7%) PV, and 129 (1.1%) FV were included. Average age was 53.0 +/- 18.2 and 52.8% were female. Accounting for the COVID-19 vaccination population groups in Michigan, the ED encounters/hospitalizations rate relevant to COVID-19 infection was 96% lower in FV versus UV (eB:0.04,95% CI 0.03 to 0.06, p <0.001) in negative binomial regression. COVID-19 EC visits rate peaked at 22.61, 12.88, and 1.29 visits per 100000 for the UV, PV, and FV groups, respectively. In the propensity-score matching weights analysis, FV had a lower risk of composite disease compared to UV but statistically insignificant (HR 0.84 95% CI 0.52 to 1.38). Conclusions: The need for emergency care and/or hospitalization due to breakthrough COVID-19 is an exceedingly rare event in fully vaccinated patients. As vaccination has increased within our region, emergency visits amongst fully vaccinated individuals have remained low and occur much less frequently when compared to unvaccinated individuals. In cases of breakthrough COVID-19, if hospital-based treatment is required, elderly patients with significant comorbidities remain at high risk for severe outcomes regardless of vaccination status.