The US Food and Drug Administration (FDA) granted emergency use authorization (EUA) to two Omicron-targeting booster vaccines on Wednesday as it anticipates the potential rise of COVID-19 cases in its fall and spring.

The boosters, one by Moderna and the other by Pfizer-BioNTech, are bivalent vaccines, or “updated boosters”, that are designed to protect against both the original strain and the BA.4 and BA.5 Omicron subvariants that are dominant in the US. The FDA had previously recommended the inclusion of an Omicron component in COVID-19 booster vaccines back in June. 

Both are scheduled to be reviewed by the US Centers for Disease Control and Prevention  (CDC)Thursday. If the CDC recommends these boosters, some may even be available starting this weekend, with more to be rolled out in clinics, doctors’ offices, and pharmacies after Labor Day.

The FDA cleared the new Pfizer-BioNTech booster for people 12 and older and the Moderna shot for those 18 and up, and the CDC is expected to concur that those ages are appropriate. 

Anyone who has received the two-shot primary series of the mRNA vaccines and the single-shot Johnson & Johnson vaccine will be eligible, regardless of whether they received any booster shots. However, they should wait two months after receiving an initial vaccine or booster before receiving this new jab.

These changes would be the first since mRNA vaccines were first introduced to the US in December 2020.

“The COVID-19 vaccines, including boosters, continue to save countless lives and prevent the most serious outcomes (hospitalization and death) of COVID-19,” said FDA Commissioner Robert Califf, in a FDA news release.

“As we head into fall and begin to spend more time indoors, we strongly encourage anyone who is eligible to consider receiving a booster dose with a bivalent COVID-19 vaccine to provide better protection against currently circulating variants.”

Omicron subvariants make up more than 90% of US cases 

 While daily reported cases have consistently remained below 100,000 since mid-August, with 88,676 new cases reported as of 30 August, the country continues to average 400 to 500 deaths a day. Omicron subvariant BA.5 currently accounts for 88.7% of cases and BA.4 3.6% of cases, according to data from the US CDC. 

The Biden administration hopes that the boosters will stave off serious health outcomes.

“In terms of trying to stave off serious outcomes and symptomatic disease, one needs to refresh the immune system with what is actually circulating and so it’s a benefit-risk here,” said Peter Marks, Director of the Center for Biologics Evaluation and Research (CBER) at the FDA, in an FDA virtual news conference Wednesday morning. 

“We believe that the benefits of receiving a booster now at least two months after [their primary series] are going to outweigh the risk.”

“A big difference here is we have to be a step ahead or at least we have to try to be a step ahead because if we waited for all the proof to come in, the wave will have already passed us by and the damage will have been done,” added Califf. 

Experts concerned about lack of public enthusiasm for boosters 

However, some experts have questioned whether the American public, which has been slow to accept COVID-19 vaccines and already available boosters, will have more enthusiasm for a new round of shots.

“We already have a problem with booster acceptance,” Eric Topol, a professor of molecular medicine at Scripps Research, said in The Washington Post. 

If that is exacerbated by the paucity of human data for the new shots, “I think that would be unfortunate,” he added. 

Already less than half of those fully vaccinated in the US – over 108 million people – have received a 1st booster dose, according to data from the CDC. And while the US has vaccinated two-thirds (67.4%) of its eligible population, this percentage is far lower than several other countries, including the United Kingdom, China, and Canada. 

 The FDA had cleared the new boosters on the “totality” of the evidence, which included human studies of earlier experimental bivalent shots, such as one against BA.1, the first omicron subvariant, and the overall record of the shots since December 2020. 

It also considered mouse data on the new booster, concluding the shots generated a strong antibody response against the variants.

But the lack of human data on the shots has raised concerns among health experts. 

“The mouse data are helpful,” said Michael Osterholm, Center for Infectious Disease Research and Policy at the University of Minnesota, “but the reason to have data for humans is to say the immune response is as good or better” as the one triggered by the original vaccine or an alternative.

“We don’t have data to support that the BA.4/BA.5 vaccine is superior.”

But Dr Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, felt that the updated boosters will be helpful even if an “out of left field” variant emerges that is different from BA.4 and BA.5.

“Any boost of immunity will have some degree of cross-reactivity even against a new variant,” Fauci said.

The FDA, in its news release, remained confident in its decision to grant an EUA.

“The FDA has extensive experience with strain changes for annual influenza vaccines. We are confident in the evidence supporting these authorizations,” said Peter Marks.

“The public can be assured that a great deal of care has been taken by the FDA to ensure that these bivalent COVID-19 vaccines meet our rigorous safety, effectiveness and manufacturing quality standards for emergency use authorization.”

Image Credits: Marco Verch/Flickr, US CDC , US CDC.