New York, NY—In a trial to see how effectively Paxlovid helped prevent infection in adults who had household exposure to COVID-19, the risk was reduced by 32% and 37% in adults who received the drug for 5 and 10 days, respectively.

Pfizer, Inc. reported, however, that the results were not statistically significant and that the primary endpoint of reducing the risk of confirmed and symptomatic COVID-19 infection in adults who had been exposed to the virus through a household contact was not met.

Pfizer shared top-line results from the phase II/III Evaluation of Protease Inhibition for COVID-19 in Post-Exposure Prophylaxis study evaluating Paxlovid, a combination of nirmatrelvir (PF-07321332) and ritonavir tablets, for postexposure prophylactic use.

The data from 2,957 adults were evaluated for the top-line report. Enrolled in the study were adults with a negative SARS-CoV-2 rapid antigen test result and who were asymptomatic household contacts with exposure within 96 hours to an individual who was symptomatic and recently tested positive for SARS-CoV-2.

Each patient was randomized (1:1:1) to orally receive twice daily one of the following: (1) Paxlovid for 5 days followed by placebo for 5 days, (2) Paxlovid for 10 days, or (3) placebo for 10 days.

Recruitment began in September 2021 and was completed during the peak of the COVID-19 Omicron wave.

Pfizer said safety data were consistent with previous studies and that analyses of all secondary endpoints and subgroups are continuing. Results will be included in the publication or presentation of the final study results.

"We designed the clinical development program for PAXLOVID to be comprehensive and ambitious with the aim of being able to help combat COVID-19 in a very broad population of patients," stated Albert Bourla, chairman and CEO of Pfizer. "While we are disappointed in the outcome of this particular study, these results do not impact the strong efficacy and safety data we've observed in our earlier trial for the treatment of COVID-19 patients at high risk of developing severe illness, and we are pleased to see the growing global use of PAXLOVID in that population."

Paxlovid is currently approved or authorized for conditional or emergency use in more than 60 countries across the globe to treat high-risk COVID-19 patients. In the United States, it has emergency-use authorization for the treatment of mild-to-moderate COVID-19 in adults and pediatric patients (aged 12 years and older weighing at least 40 kg) with positive results of direct SARS CoV-2 viral testing and who are at high risk for progression to severe COVID-19, including hospitalization or death.

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