An FDA advisory panel on Tuesday voted 13-10 to recommend Merck's antiviral pill, molnupiravir, for emergency use, and the agency is also reviewing a separate antiviral pill developed by Pfizer.

7 reasons why Merck's antiviral Covid-19 pill is a bigger deal than you think

2 antiviral pills could soon be available to the public

In October, Merck and Ridgeback Biotherapeutics released their interim analysis of a Phase 3 clinical trial showing that their oral antiviral drug molnupiravir reduced the rate of hospitalization or death by roughly 50% in participants with mild or moderate Covid-19. The drug was most effective when given early in the course of treatment—within five days of symptom onset—and was effective regardless of whether patients had the delta or other coronavirus variants.  

Pfizer's antiviral Covid-19 pill is a big deal. Here's why.

Separately, Pfizer's antiviral pill, Paxlovid, is a protease inhibitor that blocks a key enzyme that the coronavirus needs to replicate. In a trial of more than 750 people, Paxlovid was found to reduce the risk of hospitalization and death from Covid-19 by 89% when given within three days of symptom onset. According to Pfizer, Paxlovid was also found to be active against multiple variants of the coronavirus, including the delta variant, in lab testing.

On Tuesday, an FDA advisory committee reviewed molnupiravir for possible emergency use in the United States. According to the New York Times, the drug could receive emergency use authorization (EUA) this week—and Pfizer's antiviral treatment may not be far behind.

Details on FDA's evaluation of molnupiravir's safety and efficacy

Ahead of the vote on Tuesday, FDA staff released an addendum to its original briefing of Merck's drug that highlighted that "the review issues and benefit/risk assessments may [...] differ from the original assessments provided in the briefing document which was based on the interim analysis." Specifically, the agency cited Merck's full results from its Phase 3 clinical trial, released last week, which showed that in over 1,400 adults, the drug reduced the combined risk of hospitalization and death by 30%—a decline from the 50% reduction initially reported by Merck in the interim analysis submitted with its EUA request.

The FDA briefing also evaluated risk management strategies regarding the types of patients who could see the most benefit from the drug, MedPage Today reports. Specifically, FDA suggested that high-risk patients could be identified using the same CDC criteria used for monoclonal antibody treatments. FDA staff also suggested that vaccination status should be considered since unvaccinated individuals have a higher risk of hospitalization and death.

Further, according to ABC News, FDA scientists in the briefing identified several potential risks in the review of the drug, including potential toxicity to developing fetuses and birth defects that were identified during studies of molnupiravir in animals. In addition, FDA staff highlighted the potential risk of viral mutation associated with molnupiravir, specifically "an increased rate of amino acid changes in the SARS-CoV-2 spike protein." However, they concluded that these mutations did not appear to be connected to clinical outcomes, like hospitalization or death. 

FDA's advisory panel voted 13-10 in favor of the treatment for use in adults with mild to moderate Covid-19 who are at risk for severe disease or hospitalization, NBC News reports. According to the panel's chair Lindsey Baden, those who voted in favor of the drug thought its efficacy was "apparent, albeit with issues that have to be weighed." However, those who voted against the recommendation weren't convinced by the data and cited concerns about potential risks, including potential harm to fetuses and DNA damage, he said.

Next steps—and lingering concerns

While FDA isn't required to follow the committee's advice, it generally does. If authorized, Merck has agreed to provide the U.S. government 3.1 million courses of the drug for about $2.2 billion, the Wall Street Journal reports. The federal government is expected to allocate the pills to states to filter among pharmacies, hospitals, and doctors' offices for dispensing.

But even after the treatments are widely distributed and available for use, some experts worry it will be difficult to test and treat patients quickly enough for the drugs to be effective, the New York Times reports.

According to the Times, since these antiviral pills are intended to be taken within days of when symptoms first present, their success largely depends on early, accurate Covid-19 testing—which the United States has struggled to deliver throughout the pandemic.

And as new variants arise, the already strained testing infrastructure in the United States could be further put to the test. According to the Times, health officials must ensure that timely, affordable Covid-19 testing is available, particularly in communities that have been heavily impacted by the virus.

Your top resources for Covid-19 readiness

"People have to want to get tested, and we have to be able to get tests to people quickly," said David Boulware, an infectious disease specialist at the University of Minnesota. "Can that happen?"

According to the Times, it is not yet clear whether officials will require patients to take a certain kind of Covid-19 test before the drugs are prescribed. And there are challenges associated with each: PCR tests, the highly sensitive laboratory-based diagnostics, can sometimes take days to relay results, while rapid antigen tests are quick, but generally less sensitive.

According to Alyssa Bilinski, a public health policy expert at Brown University, "It starts with the public education such that when people start to have mild symptoms, early in the course of their illness, they think, 'This might be Covid-19, and I should get a test.'"

"Then, of course, we have to have access to tests that have to ideally be affordable. Then people need to get their test results backand they need to get them back quickly," she added. "All of this needs to happen within three to five days."

Because of their quick turnaround times, experts say rapid tests will likely play an important role in the rollout of these antiviral pills. And although there have been testing supply shortages, experts expect they will ease soon. "We're optimistic that the production capacity from both the big players, like Abbott and Quidel, as well as some of the newer smaller players are all hitting the ramp up phase at this point," said Nathaniel Hafer, a molecular biologist at UMass Chan Medical School.

Ultimately, "[t]he idea is access," said Michelle Barron, senior medical director of infection prevention and control for UCHealth. "The whole notion of this is, How can we keep people from progressing and ending up in the hospital?" (Robbins/Zimmer, New York Times, 11/30; Walker, MedPage Today, 11/29; Perrone, ABC News, 11/26; Anthes, New York Times, 11/29; Hopkins/McKay, Wall Street Journal, 11/30; Lovelace, NBC News, 11/30)