Paxlovid, the Covid-19 treatment made by Pfizer, reduced hospitalizations and deaths in older patients during the Omicron surge in Israel earlier this year, but made no difference for patients under 65 at high risk for severe disease, new research has found.
The study is one of the first published examinations of the real-life effectiveness of Paxlovid against the Omicron variant, now the dominant version of the coronavirus. Pfizer’s trials of Paxlovid were conducted during a surge of the Delta variant last year, and included only unvaccinated individuals.
There have been lingering questions about how effective the medication is against the Omicron variant, and among patients who are vaccinated or have some immunity from a prior bout of Covid. The drug has been available to Americans since December.
The new study did not address another pressing mystery: how often patients experience “rebound” cases of Covid after taking the drug. Jill Biden, the first lady, exited a second isolation period on Monday after her infection returned following a course of Paxlovid.
On Friday, Dr. Ashish Jha, the White House Covid-19 response coordinator, said on Twitter that while there was confusion over who should take Paxlovid, the data still indicated that it should be administered to anyone aged 50 and older soon after they develop Covid symptoms, as well as to anyone with health conditions leaving them vulnerable to severe illness.
Although the Israeli study found that the drug had no benefit for adults aged 40 to 64 with underlying health problems, other research has suggested that it can improve outcomes. One study in Hong Kong, not yet peer-reviewed or published in a journal, reported benefits among patients aged 50 to 64.
Researchers at Massachusetts General Brigham health system reported that Paxlovid significantly reduced hospitalizations among patients aged 50 to 64, with a pronounced effect among unvaccinated individuals and those with obesity.
Dr. Jha said on Twitter that there was no reason to think the drug’s benefits would accrue only to older or more vulnerable populations. He noted that there were few side effects (the most notable is a metallic taste in the mouth), and that there was no shortage of Paxlovid in the United States.
“Of course a drug that stops virus replication in a 70 yr old will do the same in 60 yr old,” Dr. Jha wrote. Nearly 200,000 Americans aged 50 to 64 have died of Covid, he noted.
Pfizer’s own studies found that Paxlovid reduced the risk of hospitalizations and deaths by 88 percent in unvaccinated individuals at high risk for severe Covid, so long as the drug was taken within the first five days of symptom onset.
The new research, published on Wednesday in The New England Journal of Medicine, showed the drug to be effective mostly in older Covid patients.
“The big story is that it works, and saves quite a few lives and hospitalizations,” said Dr. Ronen Arbel, the study’s first author and a health outcomes expert at Clalit Health Services in Tel Aviv. “It’s very important that it’s helpful for older patients.”
Other authors included Yael Wolff Sagy, Dr. Doron Netzer and Ariel Hammerman, all affiliated with Clalit Health Services, a large health care provider in Israel. The researchers reviewed medical records of almost 110,000 members of Clalit who tested positive for Covid from January through March, when the Omicron variant was dominant.
The patients were at least 40 years old and were considered to be at high risk for severe disease. Most had either been vaccinated, previously infected with Covid, or both. The mean age of patients was 60, and more than half were women.
About 4,000 were treated with Paxlovid, and the medication was highly effective when administered to individuals 65 and over, the researchers found.
Among the 42,821 patients who were 65 and older, 766 patients who did not get Paxlovid were hospitalized for Covid, while only 11 patients who got Paxlovid were hospitalized, for a relative reduction in risk of 73 percent.
Deaths were significantly reduced in the older patients treated with Paxlovid. Only two of 2,484 treated patients died, compared with 158 of the 40,337 untreated patients, a risk reduction of 79 percent.
The drug had little effect on younger adults, however, making no significant dent in deaths or hospitalizations, which were as low in this group as among the older treated patients.
Dr. Arbel said he and his colleagues had hoped to examine the rebound phenomenon, but the symptom reporting data was not reliable enough to do so.
“I know it’s a big story in the United States, but I’m not sure anyone died or was hospitalized” after a rebound, he said. “It’s almost not relevant.”
Although the drug does not appear to have much impact on younger and midlife adults, he said some physicians may still choose to prescribe it to patients under age 65.
“For a 62-year-old unvaccinated person with complications, there may be reason to give the drug,” he said.
