The medications, developed to treat and prevent viral infections in people and animals, work differently depending on the type. But they can be engineered to boost the immune system to fight infection, block receptors so viruses can’t enter healthy cells, or lower the amount of active virus in the body.
At least three promising antivirals for covid are being tested in clinical trials, with results expected as soon as late fall or winter, said Carl Dieffenbach, director of the Division of AIDS at the National Institute of Allergy and Infectious Diseases, who is overseeing antiviral development.
“I think that we will have answers as to what these pills are capable of within the next several months,” Dieffenbach said.
The top contender is a medication from Merck & Co. and Ridgeback Biotherapeutics called molnupiravir, Dieffenbach said. This is the product being tested in the Kellys’ Seattle trial. Two others include a candidate from Pfizer, known as PF-07321332, and AT-527, an antiviral produced by Roche and Atea Pharmaceuticals.
They work by interfering with the virus’s ability to replicate in human cells. In the case of molnupiravir, the enzyme that copies the viral genetic material is forced to make so many mistakes that the virus can’t reproduce. That, in turn, reduces the patient’s viral load, shortening infection time and preventing the kind of dangerous immune response that can cause serious illness or death.
So far, only one antiviral drug, remdesivir, has been approved to treat covid. But it is given intravenously to patients ill enough to be hospitalized, and is not intended for early, widespread use. By contrast, the top contenders under study can be packaged as pills.
Sheahan, who also performed preclinical work on remdesivir, led an early study in mice that showed that molnupiravir could prevent early disease caused by SARS-CoV-2, the virus that causes covid. The formula was discovered at Emory University and later acquired by Ridgeback and Merck.
Clinical trials have followed, including an early trial of 202 participants last spring that showed that molnupiravir rapidly reduced the levels of infectious virus. Merck chief executive Robert Davis said this month that the company expects data from its larger phase 3 trials in the coming weeks, with the potential to seek emergency use authorization from the Food and Drug Administration “before year-end.”