The impact of variants and vaccination on the mortality and resource utilization of hospitalized patients with COVID-19

Background COVID-19 outcomes among hospitalized patients may have changed due to new variants, therapies and vaccine availability. We assessed outcomes of adults hospitalized with COVID-19 from March 2020-February 2022. Methods Data were retrieved from electronic health medical records of adult COVID-19 patients hospitalized in a large community health system. Duration was split into March 2020-June 2021 (pre-Delta period), July-November 2021 (Delta period), and December 2021-February 2022 (Omicron period). Results Of included patients (n = 9582), 75% were admitted during pre-Delta, 9% during Delta, 16% during Omicron period. The COVID-positive inpatients were oldest during Omicron period but had lowest rates of COVID pneumonia and resource utilization (p < 0.0001); 46% were vaccinated during Delta and 61% during Omicron period (p < 0.0001). After adjustment for demographics and comorbidities, vaccination was associated with lower inpatient mortality (OR = 0.47 (0.34-0.65), p < 0.0001). The Omicron period was independently associated with lower risk of inpatient mortality (OR = 0.61 (0.45-0.82), p = 0.0010). Vaccination and Omicron period admission were also independently associated with lower healthcare resource utilization (p < 0.05). Magnitudes of associations varied between age groups with strongest protective effects seen in younger patients. Conclusion Outcomes of COVID-19 inpatients were evolving throughout the pandemic and were affected by changing demographics, virus variants, and vaccination.