Update: Paxlovid’s failure as a preventative measure raises questions, but doctors still back it as a therapeutic

Paxlovid’s failure as a preventative measure raises questions, but doctors still back it as a therapeutic The news that Paxlovid did not work as a preventative for Covid doesn’t affect its primary use, experts say: treating people who are already sick. Matthew Herper STAT

Pfizer released news late Friday that Paxlovid, the antiviral currently subject to a big push from the U.S. government, failed to prevent people living with Covid patients from catching the infection.

The news is one of several bad headlines for the new Covid pill, but one experts say doesn’t affect the medicine’s primary use: treating people who are already sick.

Paul Sax, clinical director of the division of infectious diseases at Brigham and Women’s Hospital, said he would “absolutely” prescribe Paxlovid to people at high risk of severe disease who have Covid. “Without hesitation,” he said. “Because the net benefit in the high risk study was extremely high.”

And some experts said the results, while disappointing, are not a surprise. “Traditionally it’s been difficult to use small molecule antivirals for true prophylaxis because the biology of treating infection is different from the biology of preventing infection,” said Daniel Barouch, director of the Center for Virology and Vaccine Research at Beth Israel Deaconess Medical Center.

In the new study, Paxlovid or placebo was given to 2,957 adults who had a negative rapid antigen test and were asymptomatic, but who were living with someone who had Covid. The medicine (or the placebo) was given within 96 hours of the infected individual becoming infected. Volunteers were randomly assigned to receive either a five-day course of Paxlovid, a 10-day course, or placebo.

Patients who received the five-day course tested positive 32% less often for SARS-CoV-2, the virus that causes Covid, than those who received placebo. Those who received the 10-day course tested positive 37% less often than those who received placebo. But both of those results were not statistically significant, and may have been due to chance.

The results contrast sharply with those for monoclonal antibody drugs earlier in the pandemic, where roughly similar studies showed Regeneron’s REGEN-CoV, Eli Lilly’s bamlanivimab, and AstraZeneca’s Evusheld all reduced rates of infection by 80%.

Figuring out why may be difficult, especially until more data are available.  ...