Pfizer and rival Moderna both asked U.S. regulators this week to authorize modified versions of their booster vaccine - shots that are half the original recipe and half offer protection against BA.4 and BA.5, the newest versions of omicron.
The Food and Drug Administration ordered that recipe and now is evaluating what scientists call a "bivalent vaccine," with a decision expected soon.
The first update to the recipe is momentous but it's more of an expected next step - like how flu vaccines get updated every year - than a true next-generation shot.
Dr. Peter Marks, the FDA's vaccine chief, says the tweaked boosters could help right away - while BA.5 infections still are too high - as well as help blunt yet another winter surge.
"By changing the composition of what is in these boosters, we are able to elicit and essentially refresh the immune response," Marks told The Associated Press.
BA.5 currently is causing nearly all COVID-19 infections in the U.S. and much of the world, but current COVID-19 vaccines match the coronavirus strain that circulated in early 2020.
While those vaccinations still offer strong protection against serious illness or death from COVID-19, there's little effectiveness against infection from the wildly mutated omicron family.
The first update to the recipe is momentous but it's more of an expected next step - like how flu vaccines get updated every year - than a true next-generation shot.
Pfizer and Moderna both studied an earlier tweak to their vaccines that targets the original omicron, called BA.1, that hit last winter, plus even earlier variants.
FDA will use data from human testing of the BA.1-tweaked doses plus mice tests of the BA.5-targeted version to decide if the newest update spurs protective levels of virus-fighting antibodies.
"If we wait a few months until we have the kind of clinical data that we had before, well, you can see what happened with delta and with omicron BA.1," Marks said. "We're going to be on to the next thing."
He added: "The goal here is to use our best knowledge ... to provide people with the longest duration of protection that we can."
