The antiviral drug Paxlovid (nirmatrelvir–ritonavir) is significantly more effective in preventing hospitalization or death from omicron-related COVID-19 when taken within five days of symptom onset as recommended.

That’s according to a matched cohort study of patients in the Kaiser Permanente Southern California healthcare system during the BA.2, BA.4 and BA.5 omicron waves. Investigators examined data for more than 130,000 outpatients aged 65 years and younger. 

Levels of COVID-19 were high during the study period, as was vaccine uptake in the cohort’s Southern California setting, the researchers noted. 

Early treatment

Patients with COVID-19 who received Paxlovid at any point after diagnosis had 54% overall lower incidence of hospitalization or death within 30 days of a positive SARS-CoV-2 test than those who did not take the drug. But efficacy soared to 80% when it was dispensed within five days of symptom onset, and even higher (90%) in a subgroup of those patients who received the drug on the day of their test, investigators found. 

“In conjunction with vaccination as a primary prevention strategy, nirmatrelvir–ritonavir can help to prevent hospital admission or death when used to treat COVID-19 in an outpatient setting in the context of high seroprevalence and wide uptake of COVID-19 vaccines,” wrote the investigators, from the University of California, Berkeley and drugmaker Pfizer. Early treatment was associated with the greatest clinical benefit, they added.

The findings underscore “the continued need for prompt testing and treatment among people at high risk of progression to severe COVID-19,” the researchers concluded.

Paxlovid was authorized for emergency use in 2021 for the treatment of mild-to-moderate COVID-19 in adults and pediatric patients who are at high risk for progression to severe COVID-19. Advisers to the Food and Drug Administration on March 16 recommended that the drug be fully approved for use in adults aged 50 years and older who are vulnerable to severe disease.

The current study was published in The Lancet.

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