Pfizer announced Friday that a recent large, late-stage trial found that its COVID-19 antiviral pill, Paxlovid, failed at preventing symptomatic infection of people living with a person who has the disease.
The trial enrolled 2,957 participants aged 18 and older who live in the same household as another person who has COVID-19 with symptoms. They were given either Paxlovid or a placebo twice daily for five or 10 days.
Researchers reported that those who took Paxlovid for 5 days were 32 percent less likely to become infected compared to the placebo group. People who took Paxlovid for 10 days were 37 percent less likely to get infected. The results were not statistically significant, however, which means it could possibly be due to chance.
Paxlovid consists of two different antiviral drugs—nirmatrelvir and ritonavir. It is currently approved or authorized for conditional or emergency use in more than 60 countries to treat COVID-19 patients at high risk of severe illness.
The FDA also said that using Paxlovid in people with uncontrolled or undiagnosed HIV-1 infection "may lead to HIV-1 drug resistance."
Clifford Lane, deputy director for clinical research at NIAID, told the outlet that the issue is "a pretty urgent thing for us to get a handle on." He said the agency is discussing with scientists at the Centers for Disease Control and Prevention (CDC) about carrying out a number of possible epidemiological and clinical studies to learn about these rebound cases.
Paul Sax, a Harvard Medical School professor and the clinical director of the Division of Infectious Diseases at Brigham and Women’s Hospital, told Bloomberg that if people have symptoms that worsen after taking Paxlovid, "it’s probably still COVID."