CNN  — 

The antiviral medication Paxlovid appears to be most effective in people whose age or underlying health puts them at high risk for becoming severely ill with Covid-19, but it appears to be less effective for average-risk adults, drugmaker Pfizer reported.

The news is “good timing, because there is a lot of Covid out there,” said Dr. Michael Charness, an internist and neurologist at Boston’s Veterans Affairs Healthcare System. Although the drug’s emergency use authorization from the US Food and Drug Administration permits only prescribing to high-risk patients, “there is probably a more relaxed standard in the community.”

“I think this provides some clarity,” said Charness, who was not involved in the research.

In a study designed to test Paxlovid in “standard-risk” adults, Pfizer enrolled more than 1,100 people ages 18 and up. To join the study, they had to be within five days of a positive Covid-19 test and had to have symptoms. People who were fully vaccinated could join the study if they had at least one underlying risk factor for progression of their illness, such as obesity or suppressed immune function.

Half of this group was assigned to take Paxlovid twice daily for five days; the other half got a placebo.

In a news release Tuesday, Pfizer said Paxlovid was not proven to reduce all Covid-19 symptoms for at least four consecutive days in these average-risk participants. This was the main question being tested by the study.

A second question – whether Paxlovid could reduce the need for medical care – found significant benefit. The medication decreased health care visits for Covid-19, as measured in hospitalizations, emergency department or urgent care visits, or telehealth visits, compared with the placebo group.

“It helps to answer a question many of us have had about whether or not there is a reason to use for Paxlovid for our healthier patients,” said Dr. Cassandra Pierre, an infectious disease specialist and medical director of public health programs at Boston Medical Center.

Pierre, who also was not involved in the study, said it wouldn’t change what she does; she generally doesn’t prescribe Paxlovid unless her patient seems to be at high risk for Covid-19 complications.

But it does help her answer questions for people who might be wondering whether taking it wouldn’t help them feel better sooner and get back to their daily life faster.

“We see no benefit at this time from taking it, so I would recommend that they don’t at this point,” she said.

Pierre said many important questions about Paxlovid are still unanswered: Can it decrease the risk of long Covid, for example? Can it cut the chances that an infected person could pass it to someone else? She’ll keep watching for those.

In the meantime, Pierre said, she’d probably tell her vaccinated and boosted patients who catch Covid-19 to rest and treat their symptoms as they would with any respiratory virus, with over-the-counter pain relievers and herbal tea.

In terms of other outcomes, the study found a suggestion of benefits for people taking Paxlovid, but these did not pass a test of statistical significance, so they could have been due to chance alone. This can happen when the outcomes being tested – in this case, hospitalization and death – are relatively rare in all participants.

Among these:

  • Five people of 576 taking Paxlovid were hospitalized or died during the study, compared with 10 of 569 taking the placebo; there were no deaths in patients taking Paxlovid but one in the placebo group.
  • Among fully vaccinated participants, three of 361 taking Paxlovid were hospitalized or died, compared with seven of 360 on the placebo.
  • There was a 72% reduction in days spent in the hospital in people taking Paxlovid compared with those on a placebo.
  • No patients taking Paxlovid were admitted to intensive care, compared with three in the placebo group.

Dr. Ruanne Barnabus, chief of infectious diseases at Massachusetts General Hospital, says it’s possible that the study just wasn’t powered with enough people to see a difference between the two groups, given the low rates of complications for all.

“So it’s good that we have Paxlovid available for potential variants that might cause a higher complication rate in the future,” said Barnabus, who was not involved in the research. “But it’s also the first of, I hope, a pipeline of antivirals as we figure out how to better treat these infections.”

Get CNN Health's weekly newsletter

Sign up here to get The Results Are In with Dr. Sanjay Gupta every Tuesday from the CNN Health team.

Still, the results are a letdown after big benefits were reported in higher-risk people. A study of more than 2,200 patients at high risk from Covid-19 showed that Paxlovid cut the risk of hospitalization or death by 89% compared with a placebo.

Pfizer said it would stop enrolling study participants in the standard-risk group and focus instead on those at higher risk of severe outcomes, which still amounts to a substantial number of people.

“With up to 40-50% of people around the world estimated to be high risk, we believe there remains a significant unmet need for treatment options to help combat this disease, and we will continue to prioritize efforts to advance the development of Paxlovid,” Pfizer Chairman and CEO Albert Bourla said in the news release.