The CDC’s warning cited recent reports from researchers documenting some of Paxlovid’s bounces, including patients who have been vaccinated and boosted.
The CDC’s warning comes when two small but provocative new studies by different teams of researchers in Boston and New York suggest that these relapses may not be as unusual. The scientists also found that in some patients with rebound, viral levels were probably high enough to be contagious.
In addition, one study found that two patients who have inadvertently become infected with family members. In one case, an asymptomatic 67-year-old man six days after completing Paxlovid infected a 6-month-old family member. The transmission took place after the time window suggested by the CDC to isolate itself.
“Isn’t that weird? Otherwise, why are we seeing these groups?” said Dr. Michael Charness, chief of staff at VA Boston Healthcare System and lead co-author of the study, which looked at COVID infections in 10 patients between the ages of 31 and 71 who were fully vaccinated and had received at least a booster shot. The study was published online Monday and has not been peer-reviewed.
Paxlovid is a home treatment that is prescribed at the first sign of infection to patients at high risk of serious COVID complications. The treatment consists of a total of 30 pills, three pills that are taken twice a day for five days.
When Paxlovid manufacturer Pfizer received emergency use of the drug in December from federal regulators, its data indicated that about 2 percent of patients in its trial experienced a rebound, as did approximately 1.5 percent of those who received a placebo.
The Charness study does not directly refute Pfizer data, but suggests that bounces are more common. Patients in this study experienced relapse symptoms that began three to eight days after completing Paxlovid, and the symptoms lasted three to ten days.
Antigen tests performed while patients were in relapse indicated that they remained positive for an average of six days and up to day 18 after their initial positive test prior to Paxlovid.
For comparison, the Charness group looked at a separate group of COVID patients who had not taken Paxlovid: nearly 1,000 members of the National Basketball Association. None had a relapse of COVID. This data has not been published.
“We quote from the NBA data to say that this is clearly different from what was observed,” Pfizer said. Charness and NBA studies.
A Pfizer spokesman said the company continues to monitor data from its ongoing Paxlovid studies, as well as reports from doctors and bounce patients. He said all the data is “consistent with our observations” of the company’s drug trial.
The CDC’s new warning states that a relapse of COVID with a brief return of symptoms “may be part of the natural history of SARS-CoV-2 (the virus that causes COVID-19) infection in some people, regardless of treatment. with Paxlovid and regardless of vaccination status “.
Federal data show that more than 668,000 Paxlovid courses had been prescribed by May 14th. Doctors say that despite the bounces, it is an effective medicine that has kept people at risk out of the hospital.
A second study by a team of Boston researchers looked at seven patients who had recovered after taking Paxlovid and found live virus levels in three of them for nine days. One of the patient’s test samples showed live virus for 11 days after finishing Paxlovid.
“This greatly increased the suspicion that they are contagious,” said Dr. Mark Siedner, an infectious disease physician and researcher at Massachusetts General Hospital and co-author of the study, which has not been peer-reviewed.
“It simply came to our notice then. It’s just that they’re bouncing and they seem to be starting from the beginning, their virus is growing, “Siedner said.” It’s a really unique phenomenon. “
Siedner’s team found no evidence that the virus developed resistance to Paxlovid.
Siedner and other researchers say the rebound phenomenon raises urgent questions about whether patients should be treated with a longer course of Paxlovid or perhaps another drug.
The CDC alert does not definitively answer this question.
“There is currently no evidence that additional treatment with Paxlovid or other anti-SARS-CoV-2 therapies is needed in cases where a rebound of COVID-19 is suspected,” he said.
Bounces with such high levels of live viruses have made Siedner wonder if There is something about Paxlovid that could be contributing to the phenomenon.
“Does it make us wonder if we’re not using the drug properly or long enough, or is it something inherent in Paxlovid that doesn’t allow the immune system to activate?” He said.
Siedner’s team, which includes researchers from Brigham and Women’s Hospital, as well as the Broad Institute and Ragon Institute from MGH, MIT and Harvard, is launching a new study that hopes to answer some of these questions.
They will test the immune system of people who have recovered to see if the immune response of those who received Paxlovid is different from those who did not.
Dr. Kathryn Stephenson, an assistant professor at Harvard Medical School and an infectious disease physician at Beth Israel Deaconess Medical Center, is also conducting a Paxlovid study, monitoring patients who have just started antiviral with COVID tests during two or three weeks to detect them. recovery information about symptoms.
He said his studies and other small studies of dozens of people are useful, but that much larger and more rigorous studies are urgently needed to understand and address the bounces.
“I believe it is Pfizer ‘s responsibility to produce and share this data quickly: it is their drug [that received emergency use authorization,]Stephenson said.
“It’s not fair for individual doctors and researchers to try to catch up and collect this data ourselves.”
Kay Lazar can be contacted at kay.lazar@globe.com Follow her on Twitter @GlobeKayLazar.