As COVID-19 cases continue to rise, Paxlovid is being prescribed to try to keep high-risk patients out of the hospital. But the Centers for Disease Control and Prevention is warning of potential “COVID-19 rebound” after a five-day course of the treatment. 

“If you take Paxlovid, you might get symptoms again,” CDC director Dr. Rochelle Walensky told CBS News. “We haven’t yet seen anybody who has returned with symptoms needing to go to the hospital. So, generally, a milder course.”

After a patient recovers, rebound has been reported to occur two to eight days later. Still, the CDC says the benefits of taking Paxlovid far outweigh the risks. Among unvaccinated people at high risk for severe disease, it reduced the risk of hospitalization and death by nearly 90%, according to the CDC. 

Possible causes are being investigated, but a small study suggested the symptoms are coming from the same virus and not a new infection. There is currently no evidence that additional treatment is needed, according to the CDC, and Pfizer, the maker of Paxlovid, is not changing its dosage guidelines. 

Pfizer said it is currently seeing a rebound rate of about 2%, but is continuing to monitor patients

Infectious disease expert Dr. David Ho tested positive for COVID-19 after attending a conference on the virus. He took Paxlovid and his symptoms went away, but his symptoms returned days later and he again tested positive. 

“I was totally shocked. I did not expect that. And that’s because I had tested negative six consecutive days, including two PCR,” Ho, a professor of microbiology and immunology at Columbia University, told CBS News. 

So far, it appears the risk isn’t so much that patients could become very ill again, but that they might unknowingly infect someone else. If COVID-19 does return, Walensky has this advice: “They should test. They should put their mask back on. And if their test is positive, restart the isolation protocol.” 

Jon LaPook

Dr. Jonathan LaPook is the chief medical correspondent for CBS News.