A big choice is looming. And whatever version of the virus that scientists select for America’s next jab is “probably going to be the wrong one,” says Allie Greaney, who studies the push and pull between viruses and the immune system at the University of Washington and the Fred Hutchinson Cancer Center.

Unavoidably, several months will separate the selection of this autumn’s vaccine and the deployment of said shot. That’s eons in coronavirus time. Half a year ago, we were all still living in Delta’s world; now a whole gaggle of Omicrons are running the show. Any decision that scientists make in June will have to involve assumptions about how SARS-CoV-2 will shape-shift in the future, which exactly no one is eager to make. “We keep getting burned,” says Adam Lauring, a virologist at the University of Michigan. Perhaps the virus will stay on its Omicron bender, making an Omicron vaccine—a favorite for the fall’s jab jubilee—sound like a no-brainer. Or perhaps by the time summer’s through, it will have moved on to a Rho, Sigma, or Chi that sproings out from somewhere totally unexpected and undermines that Omicron shot. With so many people around the world harboring some degree of immunity, the virus is being forced to continually reinvent itself, and no one knows what new costumes it might try on next.

Our choice of fall shot, then, is inevitably going to be a gamble and a guess. But with the clock ticking down, most of the experts I’ve been talking with think an ingredient swap is wise, and probably inevitable. “We should be updating the vaccines now or yesterday,” said Jonathan Abraham, a physician and immunologist at Harvard Medical School. Modeled on the version of the virus that kick-started the crisis more than two years ago, our current crop of immunizations is still guarding against severe illness and death. But that OG variant has long since fizzled out—leaving our shots, in this one sense, frozen in the past, while the real SARS-CoV-2 continues to race ahead. A 2022 revamp might finally give our vaccines a chance to close some of that gap.