The new COVID19 pill works by creating mutations. This has some virologists worried.

Science covers the controversy around Merck’s new antiviral pill, molnupiravir, which definitely interferes with viruses’ ability to reproduce, which kills nearly all infections … but just might maybe create a new, deadlier variant:

Last month, Merck and Ridgeback officials announced results of a clinical trial that found giving the drug to COVID-19 patients early in the disease reduced their risk of hospitalization and death by 50%. The drug’s ability to mutate RNA has raised persistent fears that it could induce mutations in a patient’s own genetic material, possibly causing cancer or birth defects; studies so far have not borne out those fears.

Now, William Haseltine, a virologist formerly at Harvard University known for his work on HIV and the human genome project, suggests that by inducing viral mutations, molnupiravir could spur the rise of new viral variants more dangerous than today’s. “You are putting a drug into circulation that is a potent mutagen at a time when we are deeply concerned about new variants,” says Haseltine, who outlined his concern Monday in a Forbes blog post. “I can’t imagine doing anything more dangerous.”

He notes that patients who are prescribed antibiotics and other drugs often don’t complete a prescribed medication course, a practice that can allow resistant germs to survive and spread. If COVID-19 patients feel better after a couple of days and stop taking molnupiravir, Haseltine worries viral mutants will survive and possibly spread to others. “If I were trying to create a new and more dangerous virus in humans, I would feed a subclinical dose [of molnupiravir] to people infected,” Haseltine says.