Even against Omicron, the most heavily altered variant of concern identified to date, vaccine protection against severe disease seems extraordinarily sturdy. “I don’t think the entire population is going to need annual vaccines,” Swaminathan told me. (The important exceptions, she noted, might be vulnerable populations, among them immunocompromised people and older individuals.) And when we do need vaccine revamps, the blistering speed at which mRNA shots can be switched up will be an advantage. Because most flu vaccines need about six months to slog through the production pipeline, vaccine strains are selected at the end of winter and injected into arms the next fall. That leaves a gap for the viruses to morph even more. mRNA shots like Pfizer’s and Moderna’s, meanwhile, could—Omicron saga notwithstanding—zing from conception to distribution in about half the time, and eliminate a good chunk of the guesswork.

Some parts of this relatively rosy future may not come to pass—or at least, they could be a long way off. We just don’t understand SARS-CoV-2 as well as we do flu viruses. In most of the world, flu viruses tend to wax in the winter, then wane in the warmer months, giving us a sense of the optimal time to roll out vaccines. And flu evolution occurs in a linear, ladderlike fashion; last year’s major strains tend to beget this year’s major strains. That makes it reasonably straightforward to “predict the direction that flu viruses are going in” and design our vaccines accordingly, says Emma Hodcroft, a molecular epidemiologist at the University of Bern.

The evolution of SARS-CoV-2, meanwhile, so far looks “more radial,” Webby told me, with new variants erupting out of old lineages rather than reliably riffing on dominant ones. Omicron, for instance, wasn’t an offshoot of Delta. “If we saw ladderlike evolution, we would know we need an Omicron vaccine now,” Florian Krammer, a flu-virus expert at the Icahn School of Medicine at Mount Sinai, told me. “That’s not what we have seen.” The coronavirus has also so far been serving up new variants at an absolutely staggering clip—far faster than virologists expected it to at the pandemic’s start—and scientists are unsure whether that churn will stop.