Unvaccinated Non-Elderly Adult Population Hospitalized for COVID-19: Risk for Severe Disease and Poor Outcomes.

Introduction: Vaccination offers significant protection against hospitalization and death due to severe COVID-19. However, a significant portion of the nonelderly U.S. adult population remains unvaccinated.

Methods: This retrospective analysis of adult patients aged under 65 years hospitalized with PCR-confirmed SARS-CoV-2 between March and November 2021 assessed the age-biased risk for severe disease and outcome in non-elderly unvaccinated adults hospitalized for COVID-19. Main measures included predisposing risk factors, disease severity and progression, and outcomes in non-elderly adults compared between (1) vaccinated and unvaccinated individuals and (2) unvaccinated individuals grouped by 10-year age increment.

Results: Two hundred nineteen non-elderly adults were included; of whom, 82.6% were unvaccinated. Overall, unvaccinated patients were more likely to be obese (60% vs 29%,  < .001) while vaccinated patients were more likely to have cardiovascular disease (50% vs 29%,  = .03). Unvaccinated individuals had prolonged ICU stay (11 vs 2 days,  = .002) and overall length of stay (6 vs 5 days,  < .0001), and higher proportion requiring oxygen at discharge (54% vs 29%,  < .0001). An age-stratified analysis of the unvaccinated cohort found that the time to discharge increased with age ( = .003). Compared to unvaccinated patients aged <46 years, unvaccinated patients aged ≥46 years demonstrated 1.47- and 3.49-times higher likelihood of oxygen dependency upon discharge ( = .002) and requiring higher level of care or worse at discharge ( = .004), respectively.

Conclusion: Results from our non-elderly cohort affirm the benefit of vaccination despite a subset requiring hospitalization for breakthrough infection. In unvaccinated non-elderly adults, risk for worse outcomes and severe disease increased substantially from middle age onward and provides strong support for vaccination efforts in this population.