Study: Oral Nirmatrelvir and Severe Covid-19 Outcomes During the Omicron Surge. Image Credit: Cryptographer/Shutterstock

The effectiveness of nirmatrelvir therapy for preventing death and hospitalization due to COVID-19 in high-risk patients during the Omicron peak

In late 2021, there was a global resurgence of the 2019 coronavirus disease (COVID-19) due to the emergence of the highly transmissible severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variant Omicron. Omicron had surpassed the Delta variant by the end of December 2021. By early January, Omicron had expanded globally, even in places with high levels of pre-existing immunity.

Study: Oral Nirmatrelvir and Severe Covid-19 Outcomes During the Omicron Peak† Image Credit: Cryptographer/Shutterstock


On December 22, 2021, the Food and Drug Administration (FDA) granted an Emergency Use Authorization (EUA) for the oral antiviral nirmatrelvir for the treatment of mild to moderate COVID-19 in patients at increased risk of developing serious disease. The typical regimen for nirmatrelvir consists of five consecutive days of treatment after a positive diagnosis of COVID-19. The FDA EUA was based on the randomized, double-blind, placebo-controlled evaluation of protease inhibition for COVID-19 in high-risk patients (EPIC-HR), which looked at nirmatrelvir treatment in non-hospitalized, high-risk, symptomatic adults with COVID -19.

In a recent study posted to the Research Square* preprint server, researchers evaluated how effective nirmatrelvir is in preventing COVID-19-associated death and hospitalization in high-risk patients.

About the study

This study used data from Clalit Health Services (CHS) computerized medical records, a large healthcare facility that serves about half of Israel’s population, including nearly two-thirds of the elderly. The trial began on January 9, 2022 and ended on March 10, 2022, the first day the medication was given to CHS patients. Patients diagnosed with COVID-19 on February 24, 2022 were eligible to participate in the study.


A total of 109,213 individuals met the inclusion criteria for the study. The mean age of the study participants was 60, with 39% of the participants. Obesity, diabetes and smoking were the most common comorbid conditions. COVID-19 immunity was present in 78% of patients, acquired by prior infection, vaccination, or hybrid immunity.

During the study period, 3,939 patients in the total population received at least one dose of nirmatrelvir treatment. Participants aged 65 and older and those recently diagnosed with cancer had significantly higher admissions. Participants without pre-existing COVID-19 vaccination and members of the Arab minority group had significantly reduced admission.

The author reports the results separately for the age groups over 65 and under 65, because testing the interaction of nirmatrelvir status with other variables showed significant differences by age group.

COVID-19-associated hospitalizations occurred in 343 of 1,435 treated patients and 334 of 64,959 untreated patients among 66,394 patients aged 40 to 64 years. COVID-19-associated hospitalizations occurred in 776 of 42,819 patients age 65 and older, 14 of 2,504 treated patients, and 762 of 40,315 untreated patients. Decreased levels of immunity to COVID-19 and previous hospitalization were the characteristics most strongly associated with a high incidence of COVID-19-related hospitalizations in both age groups. In the 40-64 age group, immunosuppression was strongly associated with hospitalizations.

Hospital admissions related to COVID-19 were reported in 182 of 20,531 patients with no prior immunity and in 161 of 45,863 patients with prior immunity in patients aged 40 to 64 years. 39,513 patients with prior immunity among participants aged 65 years and older.


During the wave of Omicron variants, medication containing nirmatrelvir was associated with a significant decrease in hospitalizations and death rates for COVID-19 in individuals 65 years of age and older. Although this was an observational study, the findings and apparent potential for preventing severe COVID-19 could help decision-makers allocate limited supplies to those for whom nirmatrelvir has been shown to be successful.

*Important announcement

Research Square publishes preliminary scientific reports that have not been peer-reviewed and therefore should not be considered conclusive, should guide clinical practice/health-related behavior or be treated as established information.

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