Boston—The EPIC-HR (Evaluation of Protease Inhibition for COVID-19 in High-Risk Patients) trial found that nirmatrelvir plus ritonavir, marketed as Paxlovid, led to an 89% reduction in hospitalization or death among unvaccinated outpatients with early COVID-19.

The researchers from Brigham and Women’s Hospital and Harvard T.H. Chan School of Public Health–led researchers advised, however, that the clinical impact of nirmatrelvir plus ritonavir among vaccinated populations remained uncertain.

They sought to determine whether “nirmatrelvir plus ritonavir reduces the risk for hospitalization or death among outpatients with early COVID-19 in the setting of prevalent SARS-CoV-2 immunity and immune-evasive SARS-CoV-2 lineages.” Their population-based cohort study involved a large healthcare system providing care for 1.5 million patients in Massachusetts and New Hampshire during the Omicron wave from January 1, 2022, to July 17, 2022.

The results were published in Annals of Internal Medicine.

Included was information on 44,551 nonhospitalized adults; most (90.3%) had received three or more COVID-19 vaccine doses. The patients were aged 50 years or older with SARS-CoV-2 infection and no contraindications for nirmatrelvir plus ritonavir.

The primary outcome was defined as a composite of hospitalization within 14 days or death within 28 days of a COVID-19 diagnosis. During the study period, 28.1% of the patients were prescribed nirmatrelvir plus ritonavir, while 71.9% were not. Patients prescribed nirmatrelvir plus ritonavir were more likely to be older, have more comorbidities, and be vaccinated.

The researchers reported that the composite outcome of hospitalization or death occurred in 69 (0.55%) patients who were prescribed nirmatrelvir plus ritonavir and 310 (0.97%) who were not (adjusted risk ratio [RR], 0.56 [95% CI: 0.42-0.75]). The results also indicated that recipients of nirmatrelvir plus ritonavir had lower risk for hospitalization (adjusted RR, 0.60 [CI: 0.44-0.81]) and death (adjusted RR, 0.29 [CI: 0.12-0.71]).

“The overall risk for hospitalization or death was already low (1%) after an outpatient diagnosis of COVID-19, but nirmatrelvir plus ritonavir reduced this risk further,” the authors emphasized.

Background information in the article recounts how the oral antiviral was granted Emergency Use Authorization for treatment of mild-to-moderate COVID-19 in the United States in December 2021, and the national strategy encouraged broad use in persons with increased risk, regardless of vaccination status, to prevent hospital crowding. The World Health Organization recommended nirmatrelvir plus ritonavir in April 2022 but limited its use only for the highest-risk patients with more than a 10% probability of hospitalization. WHO also advised against use in most vaccinated and other lower risk people.

“Emerging data involving the initial Omicron variants show a potential benefit of nirmatrelvir plus ritonavir regardless of vaccination status, but only a small proportion of the eligible patient populations in these studies were treated,” the researchers advised. “A better understanding of the clinical effectiveness of nirmatrelvir plus ritonavir is needed to inform individual and public health decisions, particularly among vaccinated persons infected by Omicron strains (B.1.1.529, BA.2, BA.5, and other immune-evasive sublineages).”

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