An observational, retrospective cohort study showed that, regardless of a patient's prior SARS-CoV-2 immunity, adults ≥ 65 years of age who had received Nirmatrelvir treatment during omicron surge had significantly lower rates of hospitalization and mortality due to COVID-19 compared to younger adults who had received the same treatment. In a population with broad coronavirus immunity, Ronen Arbel et al. aimed to evaluate the efficacy of oral protease inhibitor Nirmatrelvir in averting severe outcomes during an increase of omicron variant infections.

At the beginning of the trial period, information on patients ≥ 40 years of age were gathered and determined to be eligible for Nirmatrelvir medication. With adjustments for sociodemographic variables, comorbid diseases, and prior SARS-CoV-2 immune status, a Cox proportional-hazards regression model along with time-dependent covariates was utilized to predict the relationship of Nirmatrelvir therapy with mortality and hospital admission owing to coronavirus infection.

Notably, 4% (3902 out of 109,254) of participants were treated with Nirmatrelvir during the study. The rate of hospitalization owing to COVID-19 among people ≥ 65 years of age who received treatment was 14.7 cases/100,000 person-days, compared to 58.9 cases/100,000 person-days among patients who were not treated (adjusted hazard ratio 0.27). COVID-19 death had an adjusted hazard ratio of 0.21.

In people aged 40-64 years, the hospitalization rate due to coronavirus disease was 15.2 cases/100,000 person-days who were given treatment, and 15.8 cases/100,000 person-days in  untreated people (adjusted hazard ratio 0.74). Adjusted hazard ratio for coronavirus disease-related mortality was 1.32. Patients ≥ 65 years of age who got Nirmatrelvir had considerably reduced hospitalization and mortality rates from COVID-19 than those who did not. In younger adults, no evidence of benefit was reported.