Scientists investigate perplexing 'viral rebound' COVID-19 cases after taking Paxlovid

When Laura Martin tested positive for COVID-19 during an extended stay in California last month, she was prescribed Paxlovid, Pfizer's highly acclaimed antiviral drug.
Just a day after her diagnosis, she began her five-day regimen of pills, which have been shown to dramatically reduce the risk of hospitalization and death.
Martin, a 63-year-old Boston native who now lives in Canada, said she was thrilled when her symptoms subsided.
"At the end [of treatment], on day 5, I was negative and felt totally normal like I didn't have any symptoms, so I was like, 'Wow, that's really great. What a great drug,'" Martin told ABC News.
Martin resumed her normal activities, but a week later she felt ill again. When her symptoms worsened, she tested again.
"It came back and that round two was a lot more severe than round one," Martin said. "That's like four days of much more significant symptoms than round one."
Martin's case is part of an apparently rare but increasingly reported phenomenon of COVID-19 symptom recurrence following treatment with Paxlovid. Though it's largely unknown what's causing the reported resurgence of the virus, scientists say they're investigating.
Pfizer says it takes the reported recurrences "very seriously," but that the rates are consistent with those receiving a placebo in clinical trials. Experts urge the drug's benefits in preventing hospitalizations and deaths outweigh the potential risk of a second positive test or symptom recurrence.
In an additional analysis of data from the Paxlovid clinical trial, the Food and Drug Administration (FDA) reported that most patients "had no symptoms at the time of a positive PCR test after testing negative and, most importantly, there was no increased incidence of hospitalization or death, or development of drug resistance.”
Company executives also reported this week that the use of Paxlovid continues to grow rapidly, especially as infection rates across the country rise again. In the US, use of the treatment has increased nearly tenfold in recent weeks.
The number of locations in the US with Paxlovid coverage has now grown to more than 33,000 available locations, a four-fold increase since late February. Additionally, the company reported that more than 2,200 test-to-treat locations are now open.
PHOTO: The Covid-19 treatment pill Paxlovid is seen in a box at the Misericordia hospital in Grosseto, Italy February 8, 2022. (Jennifer Lorenzini/Reuters, FILE)
"game changer"
Long heralded as a "game changer" in the fight against COVID-19, the drive to make Paxlovid available to Americans has increased in recent weeks, with the White House trying to increase supply of the treatment.
The drug, which was granted emergency use authorization by the FDA in December 2021 for people with mild to moderate COVID-19 at high risk of disease progression, is also strongly recommended by the World Health Organization. It has proven to be highly effective, leading to an estimated 89% reduction in virus-related hospitalizations and deaths.
However, in recent weeks a number of patients who have received the treatment have taken to social media to reveal what they say is a puzzling phenomenon of COVID-19 symptoms reappearing after completing the prescribed five-day treatment.
The story goes on

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