Background: Vaccination against SARS-CoV-2 is widely used and confers protection against morbidity and mortality in COVID-19. Little is known about disease severity and outcomes in fully vaccinated patients during hospitalization for COVID-19. Aim: To determine whether vaccination status and time from vaccination-to-hospitalization impacted disease severity in patients admitted with COVID-19. Methods: A multicenter retrospective cohort study was conducted on hospitalized adults with COVID-19 between January 1 and September 8, 2021, in Rhode Island, USA. Vaccination status and markers of disease severity, including C-reactive protein, D-Dimer values, and supplemental oxygen use during hospitalization, were obtained. Results: Two thousand three hundred forty-four patients were included. For every vaccinated patient, three unvaccinated patients were matched for a total of 424 patients in the analytic sample. Vaccinated patients had lower peak C-reactive protein (beta = -39.10, 95% CI [-79.10, -0. 65]) and supplemental oxygen requirements (beta = -38.14, 95% CI [-61.62, -9.91]) compared to unvaccinated patients. Patients who had a greater discrepancy between date of vaccination and admission had higher C-reactive protein (beta = 0.37, 95% CI [0.02, 0.71]) and supplemental oxygen requirements (beta = 0.44, 95% CI [0.15, 0.75]. Conclusion: Vaccination against SARS-CoV-2 was associated with a protective effect on disease severity during hospitalization for breakthrough COVID-19. Time elapsed since vaccination was associated with indicators of greater disease severity suggestive of waning protection over time.
Keywords: COVID-19; COVID-19 hospitalization; SARS-CoV-2 vaccination; breakthrough hospitalization; breakthrough infection; mRNA vaccination.