Merck’s antiviral drug is called molnupiravir and it is a series of 40 pills taken over five days. According to results reported by the company, molnupiravir reduced the risk of hospitalization and death by 30%.
While it’s believed to be relatively inexpensive to produce — global health officials hope the series can be sold in areas in need for as little as $10 — the federal government has purchased an initial supply of the drug for $700 per treatment.
“Molnupiravir induces hypermutation of the virus,” says Dr. Andrew Badley, an infectious disease specialist at the Mayo Clinic. “When the virus replicates, it makes mistakes in replication…which means it can’t work.”
Badley says this mechanism raises theoretical concerns in pregnant women, and that “molnupiravir could stimulate the emergence of different virus strains… We just don’t know yet what the effect will be in our population.”
dr. Andrew Badley
The Food and Drug Administration’s advisory committee voted on molnupiravir by 13 to 10. The committee expressed concern about the drug’s low efficacy when alternatives to monoclonal antibodies with 90% efficacy were available.
Pfizer’s antiviral drug is called Paxlovid, and patients prescribed the drug take six pills a day for five days. Results reported by the company suggest that it is three times as effective as molnupiravir, at nearly 90%.
“Paxlovid blocks protease,” Badley says, “which is a necessary enzyme in the virus life cycle.” Badley says Paxlovid “has benefited from a better understanding…of protein structure over the past few decades.”
The goal of antivirals is to reduce the progression of disease in newly diagnosed unvaccinated individuals who are at risk for poor outcomes from COVID-19.
A drawback of the antivirals is their reliance on an inexpensive, accessible, rapid and robust COVID-19 testing system, a tool that does not currently exist in the US. The drugs are only as good as a patient’s ability to quickly know if they are infected.
The picture these new treatments face is complicated by the advent of the ommicron variant, which has a large number of mutations on the spike protein. Since none of the new antivirals target the spike protein, they have the advantage of being considered unaffected by the advent of the mutant strain.
MRNA vaccinations for COVID-19 target spike protein, but it’s not clear whether the mutations in omicron affected their effectiveness.
The pills would be added to an antiviral arsenal that includes monoclonal antibody infusions made by Lilly, Regeneron and Glaxo, as well as Remdesivir by Gilead.
Infusions require a one-hour visit to participating infusion centers. If taken early enough, they generally have a good reputation for protecting against serious illness.
However, rural areas and underdeveloped countries do not have access to infusion centers. Those areas also have some of the lowest vaccination rates. Those characteristics make these prime locations for antiviral care in pill form.
Historically, antiviral pills have been considered a second-rate solution to health officials, with vaccines at the top. This is because vaccinated individuals who test positive have a vaccine-mediated immune response to keep them out of the hospital, and the vaccines have been shown to be very effective in doing just that, even in the case of breakthrough infections.
Antivirals are also seen as valuable in the care of immunocompromised individuals who have tested positive for COVID-19, given the vaccine’s weakness for those with such conditions.
“What I think will happen if the oral antivirals are approved is that it will help reduce demand,” says Dr. Raymund Razonable of Mayo Clinic, who is director of the monoclonal antibody infusion research clinic.
“There will be patients who prefer oral infusions over IV infusions, and that will reduce the burden on the clinical facilities.”
“They will conquer the same population and patients will now have a choice of whether to go for the IV infusion or oral pills, depending on their preference.”