In the two-plus years that COVID vaccines have been available in America, the basic recipe has changed just once. The virus, meanwhile, has belched out five variants concerning enough to earn their own Greek-letter names, followed by a menagerie of weirdly monikered Omicron subvariants, each seeming to spread faster than the last. Vaccines, which take months to reformulate, just can’t keep up with a virus that seems to reinvent itself by the week.
But SARS-CoV-2’s evolutionary sprint might not be the only reason that immunity can get bogged down in the past. The body seems to fixate on the first version of the virus that it encountered, either through injection or infection—a preoccupation with the past that researchers call “original antigenic sin,” and that may leave us with defenses that are poorly tailored to circulating variants. In recent months, some experts have begun to worry that this “sin” might now be undermining updated vaccines. At an extreme, the thinking goes, people may not get much protection from a COVID shot that is a perfect match for the viral variant du jour.
Recent data hint at this possibility. Past brushes with the virus or the original vaccine seem to mold, or even muffle, people’s reactions to bivalent shots—“I have no doubt about that,” Jenna Guthmiller, an immunologist at the University of Colorado School of Medicine, told me. The immune system just doesn’t make Omicron-focused antibodies in the quantity or quality it probably would have had it seen the updated jabs first. But there’s also an upside to this stubbornness that we could not live without, says Katelyn Gostic, an immunologist and infectious-disease modeler who has studied the phenomenon with flu. Original antigenic sin is the reason repeat infections, on average, get milder over time, and the oomph that enables vaccines to work as well as they do. “It’s a fundamental part,” Gostic told me, “of being able to create immunological memory.”
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