When will Americans be able to get a COVID-19 antiviral pill?

Update: The FDA authorized Pfizer's antiviral pill on December 22 — read the latest on that here. Our earlier story is below.

As the U.S. braces for a potential new wave of the virus this winter, there are promising signs that the first pill to treat COVID-19 in some at-risk Americans could be available by the end of the year. 

A panel of the Food and Drug Administration's outside advisers is scheduled to meet on November 30 to weigh a potential emergency use authorization for molnupiravir, an antiviral drug developed by Merck and Ridgeback Biotherapeutics that recently won authorization in the United Kingdom.

Merck says its drug halved the risk that adult COVID-19 patients with underlying health conditions ended up in the hospital or died from the disease. 

While Merck's pill could be the first authorized for Americans this year, other drugmakers are also pursuing experimental antiviral pills for COVID-19. 

About a month after Merck, Pfizer also asked the FDA for emergency use authorization for its pill, called Paxlovid. Pfizer is touting an 89% reduction in the risk of hospitalization or death when its drug was given to high-risk patients within three days of their COVID-19 symptoms. The company, which briefed top U.S. health officials Friday morning on its preliminary results, says it plans to submit data "as soon as possible" to the FDA.

"If this bears out, and the data hold up, and I have every reason to believe that's the case, I can see light at the end of the tunnel — and I had not been able to say that before now," Dr. David Kessler, the federal COVID-19 response team's chief science officer, told an event November 5 hosted by the University of California, Davis.

Here's what we know about what will come next: 

How soon could Americans get a COVID-19 antiviral pill?

The FDA says it will decide on whether to grant emergency use authorization for Merck's molnupiravir after a meeting of its Antimicrobial Drugs Advisory Committee at the end of November.

"We believe that, in this instance, a public discussion of these data with the agency's advisory committee will help ensure clear understanding of the scientific data and information that the FDA is evaluating to make a decision about whether to authorize this treatment for emergency use," Dr. Patrizia Cavazzoni, director of the FDA's Center for Drug Evaluation and Research, said in a statement in October.

The agency said it scheduled its meeting "as soon as possible" following Merck's submission in October, and is preparing "for a robust public discussion" with the committee. 

It is unclear if the FDA will also convene a meeting of the advisers before deciding whether to authorize Pfizer's drug. An agency spokesperson did not return a request for comment.

The advisers are expected to weigh whether the benefits of the pills seen in the clinical trial outweigh its potential risks. 

In the U.K., health authorities said their "rigorous review" concluded the drug was "safe and effective for those at risk of developing severe COVID-19 disease."

What are the side effects?

Merck says adverse events in its study were "comparable" between those who received the antiviral drug versus a placebo. 

Diarrhea, nausea, dizziness, and headache were listed among common side effects of the drug that "may affect up to 1 in 10 people." 

The company also said its studies of the drug in the lab and given to animals at longer and higher doses turned up no concerns of mutagenesis or genotoxicity, meaning it does not appear that the drug would damage the DNA of patients.

Pfizer also says adverse events from its drug were similar to the placebo, and mostly "mild in intensity." A spokesperson said Pfizer plans "to publish the full data in the near-term," saying they were "encouraged" by the safety results.

"The safety profile looks pretty clean for what I saw this morning. Some [gastrointestinal] distress, a few cases of hypertension in the treatment, I'm not sure what has to be looked at. Again, very rare, but very clean," said Kessler.

What's the difference between Merck's and Pfizer's drugs?

Both Merck's and Pfizer's antiviral drugs are swallowed in capsules for five days starting soon after higher-risk patients test positive for the virus. Both drugs are designed to reduce the risk of severe disease in the early days after infection, but they work in different ways.

Based on a drug first developed at Emory University to combat the flu, Merck's molnupiravir aims to hijack the system by which SARS-CoV-2, the virus that causes COVID-19, makes copies of itself using the body's cells. The drug inserts itself into the replication process of the virus, introducing errors that trick infected cells into making useless copies of the virus so it can't cause as much harm. 

By contrast, Pfizer says its pill aims to defeat the spread of the virus in the body by deploying a new compound that can bind to an enzyme of the virus, blocking it from replicating inside infected cells. The company has touted it as a "potential first-in-class" therapeutic designed specifically to target the virus. 

Pfizer's drug, named Paxlovid, includes a low dose of ritonavir — a medicine which is also used to treat HIV/AIDS — which Pfizer says helps prolong the drug's effectiveness in the body. 

Pfizer's drug works in a similar way to remdesivir, an antiviral which was approved by the FDA to treat COVID-19 last year, but the pills would be easier to administer than remdesivir, which must be given as an I.V. in a hospital or clinic.

While early results announced from Pfizer's and Merck's studies have focused on treating high-risk patients after they are infected with COVID, both companies are also trialing use of the pills to potentially prevent symptomatic disease in people after being exposed to someone else who is sick with the virus.

How would I be able to get a COVID-19 antiviral drug?

If the FDA signs off, doctors will be able to order the pills for their patients directly from medical distributors. 

Federal health officials say they plan to control allocations of Merck's drug, with health care providers able to order doses within caps set for each state.

In June, the Biden administration announced it had struck a deal with Merck to order enough molnupiravir to treat 1.7 million Americans. Overall, Merck told investors it will be able to produce a total of 10 million courses of the five-day treatment by the end of the year worldwide, and 20 million more next year. 

No U.S. purchase has been announced of Pfizer's antiviral so far. A company spokesperson said the drugmaker is spending $1 billion to scale up manufacturing of the drug. Pfizer expects to produce more than 180,000 packs of the antiviral by the end of the year and 21 million in the first half of next year.

The Biden administration is currently mulling whether to end a similar rationing system set up to manage supplies of moncolonal antibodies, another type of drug that's been in high demand to treat and prevent COVID-19. 

Demand is expected to be even higher for the antiviral pills, especially if another wave of the virus surges this winter. A months-long decline in cases nationwide appears to have plateaued in recent days, with new surges straining hospitals in some states. 

The pills "could be a game-changer for clinicians, because it's a lot easier to administer this than intravenously or subcutaneously," Dr. Michael Anderson, a senior adviser for the Biden administration's COVID-19 response, said at a recent town hall hosted by the consulting firm Aveshka.

"The ability to get this into patients in a much more rapid fashion, I think. is absolutely terrific," added Anderson.