Merck's little brown pill could transform the fight against COVID

The company is studying a variety of dosages, keeping a close eye on side effects, and monitoring a range of disease progressions, including following up to learn whether patients at different stages of Covid end up hospitalized, suffer an adverse event, or die. It’s also looking at whether or not molnupiravir reduces viral load—a measure of virus particles concentrated in the body after a person becomes infected. These studies could form the backbone of an emergency-use authorization submission with regulators.

In early March, results came in from a smaller study Ridgeback conducted of 202 nonhospitalized adults with Covid. Chief Medical Officer Wendy Painter, George’s wife, was listed as the lead author on findings from the study that were presented at one virtual conference. Some patients with detectable levels of virus particles saw them reduced after five days on the drug, with no major safety concerns. It was a good sign, but the study wasn’t comprehensive enough to determine efficacy on its own. “There’s a signal, there’s no denying that, but the numbers are so small that to say this is the ‘next antiviral,’ we need to be cautious of that,” says Adarsh Bhimraj, head of neurologic infectious disease at the Cleveland Clinic.

Data from Merck’s Phase II/III trials is expected in late March. Scientists are eager to find out if a reduction in viral load translates to better Covid outcomes. “We think that the more you lower the virus, the more likely it is to be beneficial,” says Rajesh Ghandi, an infectious disease physician and professor at Harvard Medical School. “We’ll also look to see, does it affect people’s clinical severity?” One reason Merck is studying molnupiravir in earlier-stage patients as well as later-stage, hospitalized ones is that interfering in viral replication might not make much difference in someone who’s already had Covid a while.