Immunity is too multifaceted, too broad, and too flexible for SARS-CoV-2 to shove us all the way down to the mountain’s base; although speedy defenders such as antibodies decline in the short term, other soldiers such as B cells and T cells can stick around for years, even decades, stowing intel on the virus so they can rise up again. These veteran fighters aren’t fast enough to stop a virus from breaching the body’s barriers. But when it does, they can trounce it before the infection gets too severe. They’re also far harder to stump than fickle, fragile antibodies; even weird morphs like Omicron are familiar-looking enough to evoke the ire of most vaccine-trained T cells and an appreciably large fraction of B cells. “That protects us, even if antibodies are lost,” says Hana El Sahly, an infectious-disease physician at Baylor College of Medicine…

What’s not certain, though, is how long SARS-CoV-2 will continue to rest on its laurels. Faced with growing population immunity, the virus is being forced to repeatedly switch up its appearance. In the span of just a few months, Omicron has already sprouted several new alphanumeric offshoots—BA.2.12.1, BA.4, and BA.5—that can dodge the defenses that even a tussle with their sibling BA.1 leaves behind. And it’s not entirely clear how wild SARS-CoV-2’s costume changes could get. Parts of the virus that scientists once thought were unlikely to change much have since transformed. This coronavirus, like others that have come before it, has shown a remarkable capacity to shape-shift when faced with immunity blockades, says David Martinez, a viral immunologist at the University of North Carolina at Chapel Hill. “There’s a lot of real estate left in spike,” he told me, “for the virus to continually evolve.” Our vaccines, meanwhile, remain modeled on a version of the virus that first infiltrated the population more than two years ago, and that has since disappeared. “Yes, vaccine effectiveness remains really high” against severe disease, even months out, even against Omicron, says Saad Omer, an epidemiologist at Yale University. But that doesn’t mean there isn’t room to relace our boots and attempt to ascend again.