Paxlovid, the five-day antiviral treatment for covid, may not reduce the risk of covid-related hospitalizations and all-cause deaths in vaccinated older adults, a new study suggests.
Paxlovid - Pfizer's combination of nirmatrelvir and ritonavir - has been found to reduce symptoms, hospitalizations and deaths in unvaccinated, at-risk patients. However, a Pfizer trial published in 2024 found the medication didn't significantly shorten the duration of symptoms in vaccinated adults.
Researchers wanted to understand if older vaccinated adults benefit from taking Paxlovid, given that age is the strongest predictor for a severe case of covid, said John N. Mafi, an associate professor of medicine at the David Geffen School of Medicine at UCLA and the lead author of the study.
But the study, which looked at patients' data in 2022 and was published in JAMA last month, found Paxlovid didn't lead to a significant reduction in hospitalizations and all-cause mortality.
"We were surprised and disappointed," Mafi said. "We concluded that it's because it's a highly vaccinated group with 88 percent fully vaccinated."
The study's results can inform patients' conversations with physicians when considering their risk of a serious case of covid and the cost of the antiviral medication, he said.
"The cost is part of the calculus because it's $1,650 per treatment course," Mafi said, which usually consists of 30 pills. "I think that needs to be part of the conversation."
A Pfizer spokesperson said in a statement that the company remains confident in Paxlovid's clinical effectiveness at preventing hospitalizations and deaths in patients at high risk of severe illness from covid-19. On their website, the company says that "being unvaccinated or not being up to date on COVID-19 vaccinations also increases the risk of severe COVID-19 outcomes."
Paxlovid did not significantly reduce the risk of hospitalization or all-cause mortality in a population of mostly vaccinated adults, ages 65 to 74, who lived in Ontario in 2022.
At best, Paxlovid reduced their risk of hospitalization by 1.3 percentage points, Mafi said. That's four times weaker than the risk reduction in Pfizer's clinical trial of unvaccinated, at-risk adults, he said.
The researchers used population-level data, and the findings do not consider a person's individual risk, Mafi said. A frail, immunosuppressed and vaccinated 70-year-old man has more reason to take Paxlovid than a vaccinated person the same age who's healthy and physically active, he said.
"If you're immunosuppressed, if you have cancer, chemotherapy, if you are frail, if you're living in a nursing home, if you have end-stage kidney disease, if you're an organ transplant recipient, those are very high-risk conditions," Mafi said. "I would be more cautious in those groups."
Researchers at UCLA and the University of Toronto examined the aggregate health data of more than 1.6 million older adults, ages 65 to 74, living in Ontario between April and November of 2022.
At the time, Paxlovid was only available for adults age 70 and older in Ontario, as well as the immunocompromised and some patients with certain risk factors. The policy created "a natural experiment" for researchers to evaluate Paxlovid's effect on older adults near the cutoff age, Mafi said.
Most of the adults studied - almost 88 percent - had received at least two doses of a coronavirus vaccine. The researchers compared the rate of hospitalizations and deaths in patients just below and above Ontario's 70-year-old cutoff and found Paxlovid wasn't associated with a significant reduction in covid-related hospitalizations or deaths.
"If you are vaccinated without additional risk factors, I wouldn't prescribe Paxlovid, and I probably wouldn't take it if I was a patient," said Peter Wu, an associate professor of medicine at the University of Toronto, who is a co-author of the study.
Wu said the next step is to understand whether vaccinated older adults who are immunocompromised or otherwise at high risk of severe disease benefit from taking Paxlovid.
Researchers used aggregate health data to study rates of hospitalizations and deaths. The data doesn't include details regarding the duration of the patients' symptoms, how soon they started taking Paxlovid, whether they kept taking Paxlovid or when they were vaccinated.
Also, the study didn't assess whether Paxlovid can shorten the duration of symptoms or reduce a person's risk of long covid, Mafi said. Ongoing trials at the Yale School of Medicine and in Britain are investigating the antiviral medication's potential effect, but results aren't available yet.
Anupam B. Jena, the Joseph P. Newhouse professor of health-care policy at Harvard Medical School, said the study is "quite a good natural experiment."
But, he said, some of the 70-year-olds prescribed Paxlovid probably got the medication because they met Ontario's age cutoff, not because of the severity of their symptoms. Paxlovid may not have been as effective for them as it would have been for a person who was sicker with covid, said Jena, who was not involved in the JAMA study.
Peter Chin-Hong, an infectious-disease specialist at the University of California at San Francisco, who wasn't involved in the research, said the population studied doesn't include people most at risk of ending up in the hospital - adults 75 and older who haven't been recently vaccinated.
"I can't extend the findings of this data to that population," Chin-Hong said. "It isn't addressing the people who are in the hospital in the last year or two."
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