It's the most effective treatment to prevent severe COVID – a pill called Paxlovid that studies show can be close to 90% effective in reducing the risk of severe disease.

And it's a global phenomenon. Pfizer, which manufactures the drug, just signed an agreement to import the drug to China, which is facing an unprecedented COVID surge this winter.

Yet here in the U.S., public health specialists say Paxlovid is underused. A poll taken in June and July by the COVID States Project, a consortium of several universities, found that among adults over 65 who tested positive since January 2022 and who are eligible for the drug because of their age, only 20% got a prescription.

What's up?

The ABCs of Paxlovid

First, let's review some basics about the drug, which came on the market in December 2021.

How does it work? As NPR reported in an earlier story: "The antiviral drug stops the virus from replicating in cells. And that could reduce the risk of long COVID as well as the risk of severe disease. "We know that one of the key factors that predict long COVID is detectable virus in the bloodstream at the time of infection," Dr. Peter Chin-Hong, an infectious disease physician at the University of California, San Francisco, wrote in an email. "So it stands to reason that interventions that prevent the virus from making more copies of itself would therefore lead to a lower risk of long COVID."

According to the prescribing guidelines, the 5-day treatment course of 3 pills, taken twice daily, should be started as soon as possible after a diagnosis of COVID-19 and within 5 days of symptom onset. Wait longer and the drug might not be effective.

Your doctor will also need to review with you all drugs you take since Paxlovid can interact with over a dozen medications and possibly cause toxicity. The potentially concerning medications include most statin drugs, which lower cholesterol, and the opioid pain reliever hydrocodone. Your doctor will determine if you can stay off any interacting drugs for 5 days or possibly take a lower dose of certain drugs while on Paxlovid.

Who can get Paxlovid?

In the U.S., not every COVID patient is eligible for a prescription. The Centers for Disease Control and Prevention recommends treatment for patients at risk of severe disease, hospitalization and death, which includes anyone who's 50 and older (risk increases with age), people who are unvaccinated and people with certain medical conditions, such as obesity, chronic lung disease, heart disease or a weakened immune system.

But exceptions can be made. A colleague who is under 50 told her doctor she was feeling worse each day after her positive COVID test and had a history of pneumonia. The doctor wrote a Paxlovid prescription.

Even if you're eligible you might have to convince a doctor to prescribe the drug. "A lot of doctors in the community and even major academic centers are reticent to prescribe [Paxlovid] out of concern that there are going to be drug interactions or think that a patient can just ride out the virus," says Dr. Priya Nori, an associate professor of medicine at the Albert Einstein College of Medicine in New York City.

There are also some side effects from Paxlovid that patients worry about and that could discourage some from seeking a prescription: a metallic mouth taste; stomach distress, including diarrhea.

But, says Michael Ganio, director of pharmacy practice and quality at the American Society of Health System Pharmacists, "a bad taste for five days is a small price to pay for a drug that can save your life."

Another cause for concern in the public could be the so-called rebound effect. A small percentage of patients, a Mayo Clinic study put it at 1%, can see COVID symptoms diminish during a course of Paxlovid but then return 2 to 8 days after finishing the medication. Are you contagious again? Possibly, says the CDC, but still unknown. So the CDC guidance is to isolate again and/or wear a mask when you are with others.

The testing challenge

The need to have a positive test for COVID might also be a reason for the underuse of Paxlovid. Reports are that fewer people are testing if they feel symptoms such as fever, chills, sore throat and congestion. Perhaps it's due to COVID fatigue. Or people might figure that it's flu season, so maybe it's a case of the flu.

But it's not that hard to test for COVID. The do-it-yourself home antigen tests are as of this week again available for free in the U.S. – four per household – via an online request. And insurance still covers the cost of eight kits for per month for every person covered in the household.

What's more, the FDA recently extended the use-by dates for some COVID tests that have reached their expiration. You can check this chart to find out about the tests you have on hand.

The federal government also has a "Test to Treat" locator to see where you can be tested for free and, if you test positive and are eligible, leave with the drug. Spots include community health centers and some pharmacies. But even though pharmacists have been able to prescribe the drug since July, pharmacies generally don't issue prescriptions unless they have an inhouse medical clinic run by a nurse practitioner or doctor. And getting your prescription from a pharmacist — but only a pharmacist — requires some bloodwork done within the past year.

Pharmacies may also send the pills to your home for prescriptions the doctor calls in. Walgreens just announced free Paxlovid delivery via Door Dash and UberEATS; CVS will send it the same day for a fee.

Precautionary prepping for paxlovid

For those who like to plan ahead – just in case COVID were to strike – you can make life easier by keeping an up-to-date list of any drugs you take, including dosages.

Another key factor is timing. Since Paxlovid has to be taken within five days of symptoms starting to work, you might contact your doctor's office to find out what steps to take if you test positive and think you need the drug.

No doctor? Dr. Nori says to avoid the ER or urgent care centers unless those are your only choices to obtain a prescription because while there, you could be exposed to other viruses now circulating like flu and RSV.

Other options include a telehealth visit with your doctor or an online telehealth company. Check your insurer's website to see if they partner with one.

The best pill might be free

For now, Paxlovid is free for everyone in the U.S. but that could change next year, says Jen Kates, senior vice president and director of Global Heath at the Kaiser Family Foundation. And there's no shortage. Dr. Ashish Jha, White House COVID-19 response coordinator, said at a press conference on Thursday that he expects there will be plenty of Paxlovid to take the U.S. through this winter.

But the drug might not be free forever. Congress has been resistant to adding funds for COVID treatment, says Kates, so once the current Paxlovid supply purchased by the federal government is used up, people who are insured may have to pay a copay and the uninsured will have to pay full price, "which will be expensive," says Kates.

But for the moment, Paxlovid seems like a bargain. And it is indeed the best option for reducing the risk of severe disease. The last monoclonal antibody treatment for COVD-19 lost its FDA authorization last month because it is ineffective against currently circulating variants. That leaves Paxlovid; remdesivir, which requires an outpatient infusion over three days at a hospital or treatment center; and molnupiravir, which studies put at only 30% effective in treating the virus. In addition, some doctors are treating immunocompromised patients with convalescent plasma.

But if you're not in the Paxlovid demographic, remdesivir and molnupriavir are the other options available for most people right now.

We regularly answer frequently asked questions about life during the coronavirus crisis. If you have a question you'd like us to consider for a future post, email us at [email protected] with the subject line: "Weekly Coronavirus Questions." See an archive of our FAQs here.

Fran Kritz is a health policy reporter based in Washington, D.C., and a regular contributor to NPR. She also reports for the Washington Post and Verywell Health. Find her on Twitter: @fkritz