Eligibility, Side Effects and More: What to Know About Pfizer's Paxlovid COVID Pill


With COVID cases and transmission rising across the Chicago area and the U.S., many are turning to questions over treating the virus for those who contract it, including the use of an antiviral COVID pill.

Pfizer's Paxlovid pill has been used in several recent high-profile cases, including Vice President Kamala Harris.

But as more doctors prescribe Pfizer's powerful COVID-19 pill, new questions are emerging about its performance, including why a small number of patients appear to relapse after taking the drug.

Here's what we know so far.

How effective is the pill and what do we know about patients who relapse?

Experts say there is still much to be learned about the drug, which was authorized in December for adults at high risk of severe COVID-19 based on a study in which 1,000 adults received the medication.

Doctors have started reporting rare cases of patients whose symptoms return several days after completing Paxlovid's five-day regimen of pills. That's prompted questions about whether those patients are still contagious and should receive a second course of Paxlovid.

Last week, the Food and Drug Administration weighed in. It advised against a second round because there’s little risk of severe disease or hospitalization among patients who relapse.

Dr. Michael Charness reported last month on a 71-year-old vaccinated patient who saw his symptoms subside but then return, along with a spike in virus levels nine days into his illness.

Charness says Paxlovid remains a highly effective drug, but he wonders if it might be less potent against the current omicron variant. The $500 drug treatment was tested and OK'd based on its performance against the delta version of the coronavirus.

“The ability to clear the virus after it’s suppressed may be different from omicron to delta, especially for vaccinated people,” said Charness, who works for Boston's VA health system.

Could some people just be susceptible to a relapse? Both the FDA and Pfizer point out that 1% to 2% of people in Pfizer’s original study saw their virus levels rebound after 10 days. The rate was about the same among people taking the drug or dummy pills, “so it is unclear at this point that this is related to drug treatment,” the FDA stated.

Some experts point to another possibility: The Paxlovid dose isn’t strong enough to fully suppress the virus. Andy Pekosz of Johns Hopkins University worries that could spur mutations that are resistant to the drug.

“We should really make sure we’re dosing Paxlovid appropriately because I would hate to lose it right now,” said Pekosz, a virologist. “This is one of the essential tools we have to help us turn the corner on the pandemic.”

Does Paxlovid work in vaccinated individuals?

Pfizer tested Paxlovid in the highest-risk patients: unvaccinated adults with no prior COVID-19 infection and other health problems, such as heart disease and diabetes. The drug reduced their risk of hospitalization and death from 7% to 1%.

But that doesn’t reflect the vast majority of Americans today, where 89% of adults have had at least one shot. And roughly 60% of Americans have been infected with the virus at some point.

“That’s the population I care about in 2022 because that’s who we’re seeing -- vaccinated people with COVID -- so do they benefit?” asked Dr. David Boulware, a University of Minnesota researcher and physician.

There's no clear answer yet for vaccinated Americans, who already have a hospitalization rate far below 1%.

That may come from a large, ongoing Pfizer study that includes high-risk vaccinated people. No results have been published; the study is expected to wrap up in the fall.

Pfizer said last year that initial results showed Paxlovid failed to meet the study’s goals of significantly resolving symptoms and reducing hospitalizations. It recently stopped enrolling anyone who's received a vaccination or booster in the past year, a change Boulware says suggests those patients aren’t benefitting.

At a minimum, the preliminary data should be released to federal officials, Boulware said. “If the U.S. government is spending billions of dollars on this medicine, what’s the obligation to release that data so that they can formulate a good policy?"

Can the pill be used to prevent COVID infection?

Pfizer recently reported that proactively giving Paxlovid to family members of people infected with COVID-19 didn’t significantly reduce their chances of catching it. But that's not the end of the story. Pfizer is studying several other potential benefits of early use, including whether Paxlovid reduces the length and severity of COVID-19 among households.

“It's a high bar to protect against infection but I’d love to see data on how Paxlovid did against severe disease because it may be more effective there,” said Pekosz.

How many doses do you need if you take the pill?

Paxlovid consists of three three pills taken twice a day for five days.

Who is eligible to take the pill?

Paxlovid was approved for emergency use in those 12 years and older, weighing at least 88 pounds who are at high risk of progressing to severe disease.

"Patients in the authorized population with a risk factor for progression to severe COVID-19 are eligible for Paxlovid under the EUA even if they are fully vaccinated," the FDA stated. "Patients do not have to have more than one risk factor to be considered 'high risk.'"

Are there any side effects?

According to Pfizer, possible side effects of Paxlovid are: 

  • Allergic Reactions. Those who experience a reaction are urged to stop taking Paxlovid and call a healthcare provider. Symptoms of an allergic reaction include: 
    • hives
    • trouble swallowing or breathing
    • swelling of the mouth, lips, or face
    • throat tightness
    • hoarseness
    • skin rash
  • Liver Problems. Symptoms of liver problems such as loss of appetite, yellowing of your skin and the whites of your eyes (jaundice), dark-colored urine, pale-colored stools and itchy skin, or stomach area (abdominal) pain are possible. Pfizer urged anyone experiencing these symptoms to contact their doctor as soon as possible.
  • Resistance to HIV Medicines. Use of the drug may lead to some HIV medicines not working as well in the future in those who have an untreated HIV infection.
  • Altered sense of taste 
  • Diarrhea 
  • High blood pressure 
  • Muscle aches 

Pfizer warned additional side effects could also be possible.

NBC Chicago/Associated Press
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