Some Americans will soon be able to get another shot of the bivalent COVID-19 vaccines, the Food and Drug Administration authorized Tuesday, including seniors ages 65 and older and people with compromised immune systems.

Seniors can get the dose as early as four months after their first shot of bivalent vaccine. Immunocompromised Americans can get more doses as early as two months after.

These additional shots will come from the same Moderna or Pfizer-BioNTech vaccines that were updated last year for the BA.4 and BA.5 variants of Omicron. 

As with previous changes, vaccinators can administer doses only after the Centers for Disease Control and Prevention issues updated recommendations. CDC Director Dr. Rochelle Walensky is expected to sign off on these changes this week.

The FDA’s new authorizations come as part of a sweeping set of revisions to streamline the myriad of immunization schedules that had been laid out for Moderna and Pfizer-BioNTech, moving them close to the annual seasonal flu shot.

“At this stage of the pandemic, data support simplifying the use of the authorized mRNA bivalent COVID-19 vaccines and the agency believes that this approach will help encourage future vaccination,” the FDA’s top vaccines official Dr. Peter Marks said in a release announcing the decisions.

However, Marks cautioned that the FDA is still waiting for a June meeting of its outside advisers to decide whether COVID-19 vaccine booster shots will be needed annually going forward for future seasons. 

“Is it possible that this will be something that will happen on a regular basis? It is, but that is something for discussion at the advisory committee,” Marks told reporters Tuesday.

Around 20% of adults and 43% of seniors have gotten their first bivalent vaccine dose so far, according to the CDC’s figures. 

Additional shots have already been cleared in some countries abroad. The United Kingdom began offering second doses of bivalent vaccine this month to some vulnerable residents, like those 75 and older.

Asked about the delay for rolling out additional shots in the U.S., Marks said the FDA needed additional time to complete “a very major action of consolidation” across all mRNA shots as well as to vet data on the second boosters.

“That time gave us a good chance to look at data, some of which have only recently come out in the public, to be able to feel comfortable that this is a reasonable thing to do,” said Marks.

The CDC said last week in a filing that officials had decided “late Monday” to convene a meeting of its outside vaccine advisers, the Advisory Committee on Immunization Practices, to weigh all of the FDA’s changes. The panel is only scheduled to discuss, but not formally vote, on COVID-19 vaccines.

“The meeting is critical in order for the rationale for these changes to be conveyed to the public in a timely and efficient manner,” the CDC said.

Changes for the unvaccinated

First backed by a panel of the regulator’s outside vaccine advisers back in January, authorities also will allow still-unvaccinated Americans to bypass the two original monovalent shots that were designed to target the original strain of the virus earlier in the pandemic.

Instead, most Americans would only need one bivalent shot a year to stay up to date, regardless of what they got in previous seasons.

Young children who were never vaccinated before would still need two doses of Moderna or three doses of Pfizer-BioNTech for their initial bivalent shots.

“Evidence is now available that most of the U.S. population 5 years of age and older has antibodies to SARS-CoV-2, the virus that causes COVID-19, either from vaccination or infection that can serve as a foundation for the protection provided by the bivalent vaccines,” Marks said.

The Biden administration has been working to phase out supply of its earlier monovalent COVID vaccines, which are no longer being produced and are due to expire. 

Unvaccinated adults will still also be able to elect to get their initial shots from the original Novavax or Johnson & Johnson supplies for now, although the CDC warned jurisdictions earlier this year that all remaining stocks of Johnson & Johnson’s vaccine are set to expire next month. 

Novavax’s vaccines had also been due to expire, although the Biden administration shored up supply with more new doses in February.

Updating for new variants

The FDA’s announcement comes ahead of key decisions expected next month over what variants the bivalent vaccines should be updated to target next season. That would give companies just enough time to scale up production of revisions before the fall and winter.

A panel of the World Health Organization’s scientists have already announced plans to weigh revisions next month as well, not unlike the annual process for coordinating updates to seasonal flu shots around the globe.

All infections in the U.S. right now are still being driven by XBB.1.5 variant, a descendant of two Omicron strains, the CDC estimates. XBB.1.5 was dominant over the winter and did not appear to drive more severe disease or worse vaccine effectiveness relative to earlier Omicron variants.

A handful of new siblings are being tracked climbing around the country. XBB.1.16 is the largest, at 7.2% of new infections nationwide. That strain has a mutation that could lead to some worse infectivity and disease, but authorities think it is overall largely “very similar” to earlier variants.

“It’s not clear that there’s something new besides what we have circulating currently and what’s dominant to pick,” Marks said April 4 at a session hosted by the World Vaccine Congress.

He acknowledged it was possible SARS-CoV-2 could again evolve unpredictably, long after officials have already locked in their picks for shots in the fall. 

“We may have a variant that will come out, that will emerge over the summertime, that may become dominant, that might not be as well neutralized by whatever we pick,” Marks said.