Antiviral medications have been around since the 1960s in the form of pills, intravenous solutions, ointments and even eye drops. They exist for only a handful of viruses, including H.I.V., the herpes simplex viruses, hepatitis B and C viruses, influenza A and B, and now the coronavirus.
Tamiflu, one of the most well-known antivirals, can minimize flu symptoms and shorten the course of illness when taken within a few days of getting sick. It can also be used prophylactically (in nursing home residents, for example) to prevent viral spread during outbreaks. Other antiviral therapies, like those for H.I.V. and hepatitis C, can be taken chronically, even in the absence of symptoms, to prevent the disease from progressing and to curtail symptom flares.
Most antivirals work by suppressing a virus’s ability to infect and multiply in your cells, said Dr. Rajesh Gandhi, an infectious diseases physician at Massachusetts General Hospital. This helps the body fight off an active infection by easing the symptoms and shortening the length of the illness.
But the exact way an antiviral does this depends on the treatment you use. Some antivirals prevent viruses from spreading to healthy cells by blocking the receptors on cell surfaces. Others inhibit the machinery that a virus needs to make copies of itself once it has already barged inside your cells. Because of this, it has been notoriously difficult for researchers to develop antiviral medicines that blunt viral replication without harming the human cells they hide inside, Dr. Gandhi said.
There are two oral antiviral therapies currently available to treat Covid-19 in the United States.
One, called Paxlovid, was developed by Pfizer and was the first oral treatment authorized for high risk Covid-19 patients ages 12 and older in December. It is prescribed as three pills taken twice a day for five days.
The second drug, called molnupiravir, was developed by Merck and was granted emergency use authorization just one day after the Pfizer treatment in December. Molnupiravir, taken as four pills taken twice a day for five days, is available for high-risk adults ages 18 and older.
(The Food and Drug Administration has also cleared an intravenous antiviral medication from Gilead Sciences called remdesivir, but it is most often administered at a clinic or infusion center.)
Both Paxlovid and molnupiravir have been shown to reduce hospitalization and death from Covid-19 if taken early on in the course of an infection. “They are most effective when used within a few days of the onset of symptoms,” Dr. Gandhi said.
In a Pfizer trial published in December and conducted before the Omicron wave, Paxlovid reduced the risk of hospitalization and death in high-risk, unvaccinated people by 88 percent when given within five days of symptom onset.
Molnupiravir, however, has been shown to be less effective. One analysis from Merck, also published in December, showed that it reduced the risk of hospitalization and death in high-risk, unvaccinated adults with Covid-19 by only 30 percent if taken within five days of symptom onset.
Because of this lower efficacy, Dr. Gandhi said that “most clinicians, including myself, prefer Paxlovid if it’s available and if a person doesn’t take any other medications that make Paxlovid a problem for them.”
Not everyone who tests positive for Covid-19 will get a prescription for antiviral pills, said Dr. Annie Luetkemeyer, a professor of infectious diseases at the University of California, San Francisco. To be eligible, you must test positive and have symptoms that started within five days or fewer. You must also be at increased risk of developing severe Covid-19.
Those who are asymptomatic, or who have symptoms but are not higher risk, will not be eligible.
While this may seem like very specific criteria, many people in the United States have medical conditions that would qualify them for the high-risk category, Dr. Luetkemeyer said. That includes all adults 65 and older, as well as those of any age with certain health conditions like heart disease, cancer, diabetes or obesity, she said.
It’s important, though, that you get treatment within five days of the start of your symptoms. “That’s pretty soon because people often don’t test the first day they have symptoms,” Dr. Luetkemeyer said. “You might feel a little bit lousy and think maybe you just have a cold that’ll go away.” But if you wait more than five days, you will no longer be able to take the oral medicines, she said.
And while federal guidelines prioritize treatment for those who are unvaccinated or who are not fully vaccinated and boosted, your vaccination status will not affect your eligibility.
First, you must test positive with a P.C.R. or rapid test. This can be done at home, at a regular health care provider’s office, at a testing site or at one of the pharmacy chains, community health centers, long-term-care facilities or Veterans Affairs clinics participating in the “test to treat” program.
If you test positive at a participating location that dispenses antivirals and has an authorized medical provider, you can get a Covid-19 pill prescription (if eligible) and fill it on the spot. If you test positive at a different testing site or through an at-home testing kit, you can schedule an online or in-person visit with a provider at a “test to treat” location to get and fill a prescription as well.
And just like with other medications, your regular health care provider can call in a prescription to a pharmacy for you, said Kuldip Patel, the senior associate chief pharmacy officer at Duke University Hospital in North Carolina. A federal “test to treat” website, expected to go live soon, will include locations that test for the coronavirus and dispense antiviral treatments on the spot.
Covid-19 antiviral pills are free of charge — for now.
This may change once federal supplies start to run out. The pandemic relief money that covered Covid-19 testing and treatment for the uninsured ended late Tuesday, and it is unclear if Congress will approve new funding to extend the program.
Most people who take Paxlovid don’t experience serious side effects, though some may have diarrhea, muscle pain or an altered sense of taste. These, coincidentally, can also be symptoms of Covid-19, Dr. Luetkemeyer said.
“We do adjust the dose if someone has advanced kidney disease,” she added. “And if they have serious liver disease, we don’t recommend Paxlovid to them.”
Certain medications or supplements, including painkillers, statins and even St. John’s Wort, may have adverse interactions with Paxlovid. So you may be advised to hold off on taking them for a week while being treated, Dr. Gandhi said. But for some medications, like drugs that regulate heart rhythm, abstaining for a week may not be possible. In those cases, your doctor may recommend molnupiravir for Covid-19 instead.
Molnupiravir has no known interactions with other medications, Dr. Gandhi said. But possible side effects can include diarrhea, nausea and dizziness. The drug is not authorized for anyone under 18 years old because it may affect bone and cartilage growth. And molnupiravir cannot be used during pregnancy because of the potential harm to the fetus. For this reason, doctors may also recommend that sexually active men and women of childbearing age use contraception during treatment and for a period afterward (three months for men and four days for women). Those who are breastfeeding should consider pumping and discarding breast milk during treatment and for four days after the last dose.
Absolutely. Experts recommend that everyone, regardless of whether you’ve had Covid-19 or received antiviral medication in the past, get a primary vaccine series and booster shot to protect against the coronavirus. (Some people with weakened immune systems are now eligible for a fourth dose.)
“These medications are not meant to be a substitute for vaccination,” Dr. Luetkemeyer said. Nor are they meant to be a substitute for isolation if you’re sick with symptoms, she added. You should still follow the same isolation guidelines as everyone else to reduce the chances of infecting others.