Pfizer Announces EPIC-PEP Phase II/III Trial of Paxlovid for Post-Exposure Prophylaxis Did Not Meet Primary Endpoint

On April 29, Pfizer issued a press release announcing the results of the Phase II/III clinical trial (EPIC-PEP) for the use of its COVID-19 oral medication Paxlovid (nirmatrelvir + ritonavir) in post-exposure prophylaxis. The trial did not meet its primary endpoint of reducing the risk of confirmed infections in adults exposed to the coronavirus through household contact.

The EPIC-PEP study enrolled 2,957 adults who tested negative for the COVID-19 antigen and had been exposed within 96 hours to a symptomatic individual with a positive antigen test. Participants were randomly assigned in a 1:1:1 ratio to receive one of the following treatments twice daily: (i) 5 days of Paxlovid + 5 days of placebo, (ii) 10 days of Paxlovid, or (iii) 10 days of placebo.

The results showed that, compared with the placebo, the risk of infection in adults who received Paxlovid for 5 days and 10 days was reduced by 32% and 37%, respectively, but it was not statistically significant and did not reach the primary endpoint. In terms of safety, it was basically consistent with the clinical trials conducted before. The analysis of all secondary endpoints and subgroups is ongoing.

Pfizer CEO Albert Bourla stated, "We have designed a comprehensive clinical development plan for Paxlovid aimed at helping a wide range of patients combat the COVID-19 virus. Although we are disappointed with the results of this study, it does not affect the strong efficacy and safety data of Paxlovid observed in earlier trials, and we are pleased to see an increasing number of people worldwide using Paxlovid."

Paxlovid is a combination drug consisting of the 3CL protease inhibitor nirmatrelvir and a low dose of ritonavir (Ritonavir). It is administered orally to COVID-19 patients in the form of 300mg (two 150mg tablets) of nirmatrelvir combined with one 100mg tablet of ritonavir. The dosage is given twice daily for five days. In December 2021, the drug received Emergency Use Authorization (EUA) from the FDA for the treatment of non-hospitalized patients aged 12 years and older with mild to moderate COVID-19 who are at high risk of progressing to severe disease. On February 11 this year, Paxlovid received conditional approval for import by the Chinese drug regulatory authority for the treatment of adult patients with mild to moderate COVID-19 who have risk factors for progression to severe disease.