One in Five Paxlovid Users Experience COVID Rebound Infections
- by Amber Baker
- Published November 26, 2023
- Infections
A new study published earlier this month suggests that people who took Pfizer’s Paxlovid (nirmatrelvir-ritonavir)—an antiviral drug treatment for COVID-19—are much more likely to experience reinfection than those who did not take the drug. The study, published in the Annals of Internal Medicine, reported that one in five people who take Paxlovid could experience rebound infections.1 2
Paxlovid is not a monoclonal antibody treatment but is a protease inhibitor, which is designed to stop the SARS-CoV-2 virus from replicating by blocking protease, an enzyme the virus needs to multiply.3 Paxlovid is one of multiple antiviral drugs that researchers believe have changed the course of COVID.
Paxlovid was granted full approval by the U.S. Food and Drug Administration (FDA) in May 2022 for “treatment of mild-to-moderate COVID-19 in adults at high risk for severe disease, including hospitalization and death.” The U.S. Centers for Disease Control and Prevention (CDC) recommends the drug for anyone over age 12 who is at higher risk of COVID complications. However, Paxlovid users have reported incomplete recovery, or a “rebound” effect by testing positive again after testing negative once they have finished the five-day course of the oral drug.4
Participants in Study Who Received Paxlovid Received More Vaccinations Than Placebo Group
Researchers followed 142 people who were enrolled in an ongoing study of COVID disease from March 2022 to May 2023 in which participants received Paxlovid or a placebo. The 72 people in the study who received Paxlovid had received more vaccinations than the placebo group. The researchers, led by Mark Siedner, MD at Harvard Medical School and Massachusetts General Hospital, also confirmed from cultures of the live SARS-CoV-2 virus from rebound patients, that they were still infectious and able to spread the virus to others.1
Paxlovid Rebound Patients Harbor Live Virus in Their Noses for Up to Two Weeks
Global COVID vaccine deployment strategies relied heavily on encouraging patients to get vaccinated to “prevent infection as well as spreading infection to others.” The experimental vaccines were not the only interventions designed to prevent the spread of infection that failed. In fact, the latest study found that Paxlovid users who experienced rebound infections continued to harbor the live virus in their noses for up to 14 days.4
“Our study was small and needs to be verified, but based on our data, we need to balance the fact that Paxlovid is a very important drug and should be used in higher-risk people, with the risk of rebound in 20 percent of people,” Dr. Siedner said.4
Lead Researcher Finds Discrepancies Between Pfizer’s Studies and Other Studies on Paxlovid
Dr. Siedner also explored discrepancies between Pfizer’s initial, more conservative estimates of rebound versus higher estimates from other studies, noting that more frequent testing was key. Pfizer’s study, which was not designed to study rebound, only tested participants three times: at days five, 10, and 15 after the first positive COVID-19 test. “When you don’t sample enough, you miss the rebound, and our study was able to fill in the gaps,” Dr. Siedner said. “If you’re not studying it closely enough, you may not find it.”4
Are Pharmaceuticals Fueling the Evolution of COVID?
Reinfections and mutations have been long-standing hurdles that some researcher have concluded continue to perpetuate the evolution of the virus. In fact, another recent study links Merck’s widely-used antiviral COVID drug Molnupiravir to viral mutations that can spread between other people, raising concerns about the drug’s efficacy as well as whether it could be fueling the evolution of COVID.5
Pfizer continues to gather pediatric data in hopes of submitting Paxlovid for full FDA approval for children in the future. Dr. Siedner said the rebound infection rate for Paxlovid users might be a reason for low-risk individuals to avoid taking the drug.6
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