“If there is anything we know about viruses and antiviral drugs is that eventually we will see some sort of resistance,” Andrew Pavia, chief of pediatric infectious diseases at University of Utah Health, said in an email.

What’s less clear, Pavia and other experts say, is whether any resistant variants will spread widely. The coronavirus may have particular difficulty getting around Paxlovid compared to other drugs because patients take it for only five days and because it targets a protein the virus can’t easily change. Any mutation or modification the virus makes may impair its ability to replicate or survive.

“At some point, there will be Paxlovid-resistant virus,” said Adam Lauring, who studies RNA virus evolution at the University of Michigan. “Whether that clinically becomes a problem or not, it’s hard to say.”

As the drug becomes more widely available, though, some researchers fear we may be using it in ways that raise the risk such a strain emerges.