Some doctors have recently reported on medical blogs and social media that their Covid-19 patients have improved after taking Paxlovid — and even tested negative — only to have symptoms flare up again a few days later. The rebound may occur just four or five days after treatment, although symptoms appear to be milder the second time around. You may develop a sore throat, runny nose or chills, for instance. But there is not enough data yet for experts to say how often this phenomenon occurs or who’s at risk of a rebound.
Only one case of this Paxlovid rebound has been carefully studied so far and published in a medical preprint. Researchers at the V.A. Boston Healthcare System reported that a 71-year-old man, who had been vaccinated and boosted, received Paxlovid the day he tested positive for Covid-19. Two days later, the patient felt better and remained symptom free for about a week. However, his symptoms returned on Day 9 and did not fully resolve until Day 12. Genetic sequencing revealed that the same coronavirus that caused the initial infection had multiplied and come surging back.
The study indicates that the rebound was not caused by a re-infection, a different variant or resistance to the antiviral drug.
Instead, experts theorize that Paxlovid suppresses the coronavirus so well that the patient’s immune system never gets a good look at the offending pathogen. So after the treatment, the immune cells and antibodies are not prepared to fight the virus, said Dr. Michael Charness, chief of staff at the V.A. Boston Healthcare System and an author of the case study.
The F.D.A. is currently investigating reports of viral rebound after Paxlovid treatment. If you experience such a rebound, you can report it to Pfizer’s portal for adverse events related to Paxlovid.
In Pfizer’s application for emergency-use authorization of Paxlovid, the company did suggest that “several subjects appeared to have a rebound in SARS-CoV-2 RNA levels around Day 10 or Day 14.” But the rebound occurred in both those who received Paxlovid and placebo treatment, the company said.
If additional studies suggest that Covid symptoms are more likely to rebound after a five-day course of Paxlovid, federal officials and health care providers may need to consider longer or repeated courses of antivirals. But more important, people may need to isolate for longer to avoid infecting others. “Maybe the prudent thing to do if you experience a rebound would be to restart isolation and wait until you test negative before going back to work,” Dr. Charness said.
If you get Covid-19, and are eligible for Paxlovid, you should not let fear of a rebound prevent you from seeking treatment. “Paxlovid is very effective at preventing progression to severe disease,” Dr. Charness said. “From what we’ve seen so far, the rebound hasn’t been severe for most people.”