The risk of a Paxlovid rebound may be higher than previously reported, according to a study published Feb. 22 in Clinical Infectious Diseases, an Oxford University Press journal.
Pfizer researchers have previously said rebound happened among 2.3 percent of Paxlovid users and 1.7 percent of the control group, but others have been wary about this figure.
The recent analysis included 170 patients who either received a placebo or nirmatrelvir and ritonavir — the two generics packaged as Pfizer's antiviral COVID-19 drug. For those who took Paxlovid, more than 10 percent had a rebound, which the study defined as when a person tests negative for COVID-19 after treatment and then experiences a "temporary return of symptoms with or without a positive test."
Of the COVID-19 patients who took Paxlovid, 14.2 percent tested positive again days after testing negative, and 18.9 percent had a symptom rebound.
This is the "best data so far on rate of symptomatic rebound after Paxlovid, despite limitations," Walid Gellad, MD, director of the University of Pittsburgh's Center for Pharmaceutical Policy and Prescribing, said on Twitter. "Not rare. Not 5 percent."
The study was conducted between August and November. Three out of the 43 people in the control group, or 7 percent, also reported a symptom rebound, while 9.3 percent had a viral rebound. For the study's next phase, the researchers will test for "any virus specific or host specific factors" into the rebound phenomenon.