This fall, millions of Americans could be ready for yet another type of COVID vaccine: their first dose that lacks the strain that ignited the pandemic three and a half years ago. Unlike the current, bivalent vaccine, which protects against two variants at once, the next one, like the first version of the shot, could have only one main component—the XBB.1 lineage spike of the world’s Omicron variants Current major clades of proteins.

That plan has not yet been determined. The FDA still has to convene a panel of experts, then is expected to make a final call on the autumn recipe next month. But several experts told me they hope the agency will follow through. Recent recommendation of the advisory group of the World Health Organization And focuses the next vaccine only on the strains currently circulating.

Change in Strategy—One of Two Kinds, From Original SARS-CoV-2 Plus Omicron To XBB.1 aloneExperts tell me it will be fleeting but wise, reflecting the world’s updated understanding of the virus’s evolution and the quirks of the immune system. “It makes a lot of sense,” said Melanie Ott, director of the Gladstone Institute of Virology in San Francisco. XBB.1 is the main coronavirus group airing today; Neither the original version nor the BA.5, the two coronavirus flavors in the bivalent shot, are meaningfully around anymore. And an XBB.1-focused vaccine may offer a particularly good shot at boosting immunity to global populations.

At the same time, the Kovid vaccines are still in a kind of beta-testing phase. Over the past three-plus years, the virus has spawned countless iterations, many of which have been very good at outsmarting us; We humans, meanwhile, are only on our third-ish attempt at designing a vaccine that can keep pace with the evolutionary sprint of pathogens. And we’re still learning a lot about the coronavirus’s capacity for flexibility and change, says Rafi Ahmed, an immunologist at Emory University. By now, it has long been clear that vaccines are essential for preventing serious illness and death, and that some cadence of boosting is necessary to keep the effectiveness of the shots high. But when the virus shifts its evolutionary strategy, our vaccination strategy must follow — and experts are still puzzling over how to account for those changes as they select shots for each year.

In the spring and summer of 2022, the last time the US was considering a new vaccine formula, Omicron was still relatively new, and development of the coronavirus seemed very much in flux. Pathogen had spent more than two years incorrectly slingshotting Greek-letter variants without a clear succession plan. Instead of accumulating genetic changes within a single lineage – a more iterative form of evolution, roughly akin to the flu strain – the coronavirus generated a bunch of distantly related variants that jockeyed for control. Delta was not a direct descendant of Alpha; Omicron was not a Delta branch; No one can say for sure what will happen next, or when. “We don’t understand the trajectory,” says Kanta Subbarao, head of the WHO advisory group convened to make recommendations on COVID vaccines.

And so the experts played it safe. including an omicron version The shot felt necessary because of how much the virus had changed. But going all-in on Omicron seemed too risky—some experts worried that “the virus would revert,” Subbarao told me, to a variant similar to Alpha or Delta or something. As a compromise, many countries, including the United States, went with a combination: half original, half Omicron, in an attempt to reinvigorate OG immunity while building new defenses against the circulating strains du jour.

and those shots Did Strengthen pre-existing immunity, as a booster should. But they haven’t sparked a new set of backlash against Omicron to the extent that some experts had hoped, Ott told me. Already trained on an ancestral version of the virus, the humans’ bodies seemed a bit myopic – re-awakening against previous variants over and over again, at the expense of new ones that could attack Omicron more powerfully. Its results were never thought to be harmful, Subbarao told me: the bivalent, for example, still broadens people’s immune response against SARS-CoV-2 compared to another dose of the original-recipe shot, And was Effective in reducing hospitalization rates, But Ahmed tells me that, in retrospect, he thinks the Omicron-only boost may have amplified that already powerful effect.

Paying close attention to XBB.1 now could save the world from falling into the same trap twice. People who receive an updated shot with only that strain will only receive the new, unfamiliar ingredient, allowing the immune system to focus on the fresh material and potentially out-compete the ancestral strain. The spike protein of XBB.1 also won’t be diluted with the older version — a concern Ahmed has with the current bivalent shot. When researchers added Omicron to their vaccine recipes, they did not double the total amount of spike protein; they reduced it to half of what it was before, Vaccine recipients left with just half the omicron-centered mRNA may have had the shot be monovalent, and perhaps have a more lackadaisical antibody response.

recent work Another reason the University of Texas Medical Branch virologist Vineet Menachery’s lab suggests was that half of the Omicron shots weren’t enough of a vaccination punch. Subvariants of this lineage, including BA.5 and XBB.1, have at least one mutation that renders their spike protein unstable—to the point where it takes longer to school than other versions of the spike protein. Seems unlikely to last long. immune cells. In a bivalent vaccine, in particular, the immune response may be biased towards non-omicron components, increasing the tendency of already immunized individuals to focus their energy on the parent strain. Menachery told me that for the same reason, even a monovalent XBB.1 may not deliver a predictable vaccination dose. but if people take it (still a big If), and hospitalizations remain low among people who are up-to-date on their shots, a one-year total-strain switch-out may also be an option for next year’s vaccine.

Omitting an ancestral strain from a vaccine is not without risk. The virus could still produce a variant completely different from XBB.1, although, at this point, that seems unlikely. For a year and a half now, Omicron has endured, and it now has the longest tenure of a single Greek-letter variant since the start of the pandemic. Even subvariants within the Omicron family seem to sprout more predictably from one another; After a long period of inconsistency, virus reshaping now seems “less jumpy,” says virologist Leo Poon of the University of Hong Kong. This could be a sign that humans and the virus have reached a dent now that the population is blanketed in a relatively stable layer of immunity. Plus, even if a stray Alpha or Delta lineage turns up, the world won’t be completely caught off guard: so many people have relied on protection against those and other previous variants that they’re probably still vulnerable to the worst of COVID. Will buffer well against rapid consequences. (However, this assurance doesn’t hold for people who still need primary-series shots, including babies born into the world every day. XBB.1 Boost A Great Option for People With Preexisting Immunity Maybe. But a bivalent that may offer more breadth may still be a more risk-adverse choice for someone whose immunological slate is blank.)

More vaccination-strategy changes will undoubtedly come. SARS-CoV-2 is still new to us; So there are our shots. But the evolution of the virus has, more recently, become flu-like, and its transmission pattern is slightly more seasonal. Regulators in the US have already announced that COVID vaccines will likely be offered every year in the fall – as have annual flu shots. Viruses are not exactly the same. But as the years go on, a comparison between COVID and flu shots may still be more apt — if, say, the coronavirus also begins to produce multiple, genetically distinct strains that can simultaneously are broadcast. In that case, getting vaccinated against multiple versions of the virus at once may be the most effective defense.

Flu shots can be a useful template in another way: Although those shots have followed broadly the same guidelines for many years, experts meet twice a year to decide which vaccines are recommended for each fall. They also need some flexibility in whether or not to update the content. Until 2012, vaccines were trivalent, containing ingredients that would immunize people against three different strains at once; Now many, including all of America, are quadriplegics — and soon, based on new evidence, researchers may be pushing them to return to the three-strain recipe. At the same time, the flu and Covid vaccines share a major drawback. The ingredients for our shots are still selected months before the injections actually reach us — leaving the immune system behind with a virus that has progressed in the interim. Until the world has something more universal, our vaccination strategies will have to be reactive, playing catch up with the evolutionary whims of these pathogens.

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