WASHINGTON ( Associated Press) — As more doctors prescribe Pfizer’s potent COVID-19 pill, new questions are emerging about its effectiveness, one of which is: Why do a small number of patients seem to relapse after taking the drug?
Paxlovid is the preferred option to combat COVID-19 due to its ease of administration at home and its impressive results in preventing a serious illness.
The US government has spent more than $10 billion to buy enough pills to treat 20 million people.
But experts say much remains to be learned about this drug, which was approved in December for adults at high risk of severe COVID-19 after a study in which 1,000 adults received the medication.
WHY DO SOME PATIENTS SEEM TO RELAPSE?
Doctors have begun to report rare cases of patients whose symptoms return days after finishing taking a five-day course of Paxlovid.
This has raised questions about whether these patients are still contagious and should receive a second course of Paxlovid.
Last week, the US Food and Drug Administration (FDA) ruled on the matter and advised against a second round of treatment because there is little risk of developing severe COVID-19 or hospitalization among patients who relapse. .
Dr. Michael Charness reported last month on a 71-year-old vaccinated patient who saw symptoms disappear but then return, along with a spike in virus levels nine days into his illness.
According to Charness, Paxlovid is still a very effective drug, but he wonders if it might be less potent against the current omicron variant.
The $500 drug treatment was tested and licensed based on its performance against the delta version of the coronavirus.
“The ability to clear the virus once suppressed may be different between the omicron and delta versions, especially in vaccinated people,” said Charness, who works for the Boston Veterans Health System.
Could some people be susceptible to a relapse? Both the FDA and Pfizer note that between 1% and 2% of people in the original Pfizer study experienced a rebound in virus levels after 10 days.
The percentage was about the same among people taking the placebo pills, “so it is not clear at this time that this response is related to drug treatment,” the FDA said.
Some experts point to another hypothesis: The dose of Paxlovid is not strong enough to completely suppress the virus. Andy Pekosz of Johns Hopkins University fears that could lead to drug-resistant mutations.
“We should make sure the Paxlovid dose is right, because I wouldn’t want us to lose it right now,” said Pekosz, a virologist. “It’s one of the essential tools we have to help us turn around the pandemic.”
HOW DOES PAXLOVID WORK IN VACCINATED PEOPLE?
Pfizer’s trials with Paxlovid were conducted in the highest-risk patients: unvaccinated adults with no prior COVID-19 infection and with other health conditions, such as cardiovascular disease and diabetes.
The drug reduced the risk of hospitalization and death from 7% to 1%.
This figure does not reflect the vast majority of Americans today, where 89% of adults have been vaccinated at least once and close to 60% of the population has been infected with the virus at some point.
“That’s the population I’m concerned about in 2022 because that’s what we’re seeing: people vaccinated with COVID, but do they benefit?” asked Dr. David Boulware, a researcher and physician at the University of Minnesota.
There is no clear answer yet for vaccinated Americans, who already have a hospitalization rate well below 1%.
The conclusion may come from a large, ongoing Pfizer study that includes high-risk vaccinated people. The results have not been published; the study is expected to end in the fall.
Last year, Pfizer said that initial results showed Paxlovid did not meet the study goals of significantly relieving symptoms and reducing hospitalizations.
It recently stopped including everyone who had received a vaccine or booster in the past year, a change that Boulware says indicates those patients aren’t benefiting.
Boulware said that, at a minimum, preliminary data should be released to federal officials. “If the US government is spending billions of dollars on this drug, is there an obligation to release that data so they can make good policy?”
CAN PAXLOVID BE USED TO HELP PREVENT COVID-19 INFECTION?
Recently, Pfizer reported that preventive administration of Paxlovid to family members of people infected with COVID-19 did not significantly reduce the chances of contagion.
But there the history not ends. Pfizer is studying several other potential benefits of early use, including whether Paxlovid reduces the duration and severity of COVID-19.
“It’s a very high standard to protect against infection, but I’d love to see data on how Paxlovid fared against severe disease, because it might be more effective there,” Pekosz said.
Matthew Perrone is on Twitter as: @AP_FDAwriter
The Associated Press Health and Science Department receives support from the Howard Hughes Medical Institute’s Department of Science Education. The Associated Press is solely responsible for all content.