Real-World Effectiveness of Nirmatrelvir/Ritonavir in Preventing Hospitalization Among Patients With COVID-19 at High Risk for Severe Disease in the United States: A Nationwide Population-Based Cohort Study

Objectives: The aim of this analysis was to describe nirmatrelvir/ritonavir real-world effectiveness in preventing hospitalization among high-risk US COVID-19 patients during SARS-CoV-2 Omicron predominance. Design: An ongoing population-based cohort study with retrospective and prospective collection of electronic healthcare data in the United States. Methods: Data for this analysis were collected from the US Optum® de-identified COVID-19 Electronic Health Record (EHR) dataset during December 22, 2021−June 8, 2022. Key eligibility criteria for inclusion in the database analysis were ≥12-years-old; positive SARS-CoV-2 test, COVID-19 diagnosis, or nirmatrelvir/ritonavir prescription; and high risk of severe COVID-19 based on demographic/clinical characteristics. Potential confounders between groups were balanced using propensity score matching (PSM). Immortal time bias was addressed. Outcome measures: Hospitalization rates within 30 (primary analysis) or 15 (sensitivity analysis) days from COVID-19 diagnosis overall and within subgroups were evaluated. Results: Before PSM, the nirmatrelvir/ritonavir group (n=2811) was less racially diverse, older, and had higher COVID-19 vaccination rates and a greater number of comorbidities than the nonnirmatrelvir/ritonavir group (n=194,542). Baseline characteristics were well balanced across groups (n=2808 and n=10,849, respectively) after PSM. Incidence of hospitalization (95% CI) within 30 days was 1.21% (0.84%−1.69%) for the nirmatrelvir/ritonavir group and 6.94% (6.03%−7.94%) for the nonnirmatrelvir/ritonavir group, with a hazard ratio (95% CI) of 0.16 (0.11−0.22; 84% relative risk reduction). Incidence within 15 days was 0.78% (0.49%−1.18%) for the nirmatrelvir/ritonavir group and 6.54% (5.65%−7.52%) for the non-nirmatrelvir/ritonavir group; hazard ratio 0.11 (0.07−0.17; 89% relative risk reduction). Nirmatrelvir/ritonavir was effective in African American patients (hazard ratio, 0.35 [0.15−0.83]; 65% relative risk reduction). Relative risk reductions were comparable with overall results across ages and among vaccinated patients. Conclusions: Real-world nirmatrelvir/ritonavir effectiveness against hospitalization during the Omicron era supports EPIC-HR efficacy among high-risk patients. Future research should confirm these early realworld results and address limitations.