Real-World Effectiveness of Nirmatrelvir/Ritonavir on Covid-19-Associated Hospitalization Prevention: A Population-Based Cohort Study in the Province of Québec, Canada.

Abstract

The nirmatrelvir/ritonavir has shown to reduce COVID-19 hospitalization and death before Omicron but updated real-world evidence studies are needed. This study aimed to assess whether nirmatrelvir/ritonavir reduces the risk of COVID-19-associated hospitalization among high-risk outpatients. This was a retrospective cohort study of SARS-CoV-2-infected outpatients between March 15 and October 15, 2022, using data from the Québec clinico-administrative databases. Outpatients treated with nirmatrelvir/ritonavir were compared to infected ones not receiving nirmatrelvir/ritonavir using propensity-score matching. Relative risk of COVID-19-associated hospitalization occurring within 30 days following the index date was assessed using a Poisson regression. A total of 8,402 treated outpatients were matched to controls. Regardless of vaccination status, nirmatrelvir/ritonavir treatment was associated with a 69% reduced relative risk of hospitalization (RR: 0.31 [95%CI: 0.28; 0.36], NNT=13). The effect was more pronounced in outpatients with incomplete primary vaccination course (RR: 0.04 [95%CI: 0.03; 0.06], NNT=8), while no benefit was found in those with a complete primary vaccination course (RR: 0.93 [95%CI: 0.78; 1.08]). Subgroups analysis among high-risk outpatients with a primary vaccination course showed that nirmatrelvir/ritonavir treatment was associated with a significant decrease in relative risk of hospitalization in severely immunocompromised outpatients (RR: 0.66 [95%CI: 0.50; 0.89], NNT=16) and in high-risk outpatients aged 70 years and older (RR: 0.50 [95%CI: 0.34; 0.74], NNT=10) when the last dose of the vaccine was received at least six months ago. Nirmatrelvir/ritonavir reduces the risk of COVID-19-associated hospitalization among incompletely vaccinated high-risk outpatients and among some subgroups of completely vaccinated high-risk outpatients.