Public Health Watch: “Rebound” COVID-19 Cases Following Paxlovid Treatment a “Scientific” But Not “Clinical” Concern

Government agencies and researchers continue to monitor the potentially troubling trend.


With COVID-19, the disease remains far worse than the cure.

That’s the case even as reports have surfaced regarding so-called “rebound” infections with Pfizer’s antiviral Paxlovid. According to media reports, a small number of COVID-19 patients treated with the drug have seen their symptoms return and even tested positive again after being negative following the 5-day course.

These reports do not outweigh clinical trial data that suggest the antiviral—developed and brought to market in record time—is nearly 90% effective at preventing serious illness and death from SARS-CoV-2 infection. Still, they are cause for concern, experts say.

Rebound infections are “a ‘scientific concern’ but not a clinical concern at this point and we need studies to understand this phenomenon,” Carlos del Rio, MD, executive associate dean, Emory School of Medicine and Grady Health System in Atlanta, told Contagion. “I would continue to prescribe the drug as indicated in the emergency use authorization.”

The US Food and Drug Administration has acknowledged that it is “aware of the reports of some patients developing recurrent COVID-19 symptoms after completing a treatment course of Paxlovid.” However, it continues to emphasize the clinical trial data demonstrating the drug’s safety and efficacy.

It has asked Pfizer, which developed and manufactures Paxlovid, to review the clinical trial data for rebound cases. However, of more than 300,000 people treated with the drug in a single database, less than 0.005% suffered a rebound infection, according to the company’s chief scientific officer Mikael Dolsten, MD, PhD, told company investors recently.

This is far less than the 2% currently cited by the FDA.

Of course, rebound infections have occurred with antibiotics over the years, but SARS-CoV-2 is a different animal. Indeed, with precise data lacking, the issue has, naturally, been debated on social media, but it’s important to note that, in this case, public health and infectious disease experts have echoed Dr. del Rio’s call for additional research. No one is calling for the drug to be pulled from the market—yet—nor questioning its therapeutic value in patients at risk for severe COVID-19.

If anything, “we need to use this drug a lot more than we are actually using it,” del Rio said. “I think most patients currently receiving Paxlovid are already vaccinated and are having breakthrough infections. That may actually be the issue.”