However, the drug remains one of the most effective ways of preventing serious illness and death

Published 11/14/23, Sarah Braner The Messenger

Viral rebound after taking Paxlovid may be more common than you thought. 

Paxlovid, developed by Pfizer, is a widely used medication to combat COVID-19 infections. It has been widely endorsed by U.S. health officials and even President Biden as a gold standard treatment for the virus.

However, some patients may experience what’s called “rebound” after taking its five day course. This is when a person’s COVID symptoms return after they are initially cleared while using the medicine.

Reports of the Paxlovid rebound first emerged in Spring 2022, when the medication first started to receive widespread use as a COVID antiviral. It left many doctors puzzled, with the mechanism of how the rebound occurred unclear to them.

Scientists have since found that the rebound is likely because some of the virus has managed to stick around despite the treatment, though according to the Centers for Disease Control and Prevention, these lingering symptoms have not caused any reported cases of severe disease. However, reports of the rebound are few and far between, with limited available data on how often this recurrence happens.

For the new study, published Monday in the Annals of Internal Medicine, researchers from Mass General Brigham analyzed data from patients from March 2022 to May 2023. 

Researchers found that 21% of 72 patients who received the Pfizer drug to fight the viral illness saw their symptoms rebound, compared to just 1.8% of the 55 people who did not use the drug. The Brigham team did note that the people who used Paxlovid were more likely to have immunosuppressive conditions, however, and it is unclear whether that played a role.

This rebound occurred without symptoms worsening, though eight of the 16 total people in the trial, 15 of whom had taken Paxlovid, who experienced viral rebound said that their symptoms came back. Notably, the infections that came back were able to replicate, meaning that these patients might still be able to spread the virus to others. The median amount of time that the people with viral rebound were shedding viruses was 14 days in the Paxlovid group and three days in the non-treatment group.

“For patients with COVID-19 at low risk for severe disease, the possibility of prolonged shedding should be factored into the consideration of potential risks and benefits of treatment,” the authors say.

However, the researchers did not find that the viruses had any mutations that granted them resistance to the drug. 

Rebound was more common in those who started Paxlovid within two days of symptoms starting compared to people who started it two or more days after symptoms started. The drug is generally supposed to be used within the first five days if symptom onset.

The exact cause of viral rebound is unknown, though the authors speculate that the current guidelines that say Paxlovid should be taken for five days might not be long enough to eradicate the virus. 

The authors stress that despite these results, Paxlovid is still a treatment worth taking to reduce the risk of a serious complication.

“This study, while informative, does not change the fact that this drug is very effective at preventing hospitalizations and death,” said Jonathon Li, M.D., one of the senior authors of the study, in a press release. “Instead, it offers valuable insights to Paxlovid patients, helping them understand what to expect and how long they might be contagious.”