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. Key point In this observational study of almost 10,000 patients hospitalized from March 2020–February 2022 with COVID-19, age and having multiple comorbidities remained consistent risk factors for mortality regardless of the variant. Vaccination was high in our hospitalized patients. Vaccination conveyed less severe illness and was associated with lower inpatient mortality.