US regulators informed COVID-19 vaccine makers on Thursday that any fall booster shots must include protection against the newest omicron relatives.
The original vaccines, according to the Food and Drug Administration, will be used for anyone who is still receiving their first series of shots. However, with immunity waning and the super-contagious omicron family of variants becoming more adept at evading protection, the FDA determined that fall boosters required an update.
The recipe: Combination shots that supplement the original vaccine with protection against the omicron relatives BA.4 and BA.5. These mutants now account for slightly more than half of all new infections in the United States.
It’s still a gamble because no one knows whether an omicron relative will remain a threat as winter approaches or if a newer mutant will take its place. And, as long as people have received the previously recommended boosters, the current Pfizer and Moderna vaccines continue to provide strong protection against COVID-19’s worst outcomes.
However, the combination approach, known as “bivalent” shots by scientists, would allow the boosters to retain the proven benefits of the original vaccine while expanding its breadth of protection. It’s a common vaccine strategy: flu shots, for example, can protect against four influenza strains and are adjusted annually based on what’s in circulation.
The FDA’s decision comes after its scientific advisers recommended earlier this week that any boosters for a fall campaign contain some form of omicron – but did not specify whether it should be the omicron mutant that caused last winter’s surge or its genetically distinct relatives.
Pfizer and Moderna were already developing and testing boosters against the first omicron mutant in preparation for an October release. They discovered that adding the extra protection was safe — and that it stimulated the production of more omicron-fighting antibodies than simply receiving another dose of today’s vaccine.
Pfizer had begun work on another experimental dose to target the newer strains that the FDA eventually chose.
“We’re still collecting data from our BA.4/5 study and will be in touch as soon as we’re ready to submit,” Pfizer spokeswoman Jerica Pitts said in an email.
Moderna informed FDA advisers that switching to even newer strains now in circulation could push back the booster update by another month. According to a company spokesperson, Moderna intends to submit its vaccine data to regulators.
The FDA’s order does not guarantee that those combination shots will be available in the fall. Manufacturers must still provide key data before the agency decides whether to approve modified boosters, and the Centers for Disease Control and Prevention must then decide how they will be used.
For the time being, an important first booster of the current vaccine is recommended for all Americans aged 5 and up. People over the age of 50 are eligible for a second booster. Authorities say omicron’s protection against COVID-19 hospitalization has slipped slightly in older adults, but a second booster can help restore it.