Pfizer and BioNTech have taken a step closer to a planned Covid-19 booster campaign this fall by completing their request for FDA emergency authorization of a version of their messenger RNA shot adapted to the prevailing omicron subvariants circulating in the U.S. The companies said Monday that upon receiving authorization, the booster shots will be available to ship immediately.

The booster shot is a bivalent vaccine designed with two main parts: one that protects against the original SARS-CoV-2 virus and the other that addresses the now dominant BA.4 and BA.5 omicron subvariants. But in seeking authorization for this booster shot, Pfizer and BioNTech are moving forward without the same level of data that backed the authorization of the original vaccine.

The only booster clinical data that Pfizer and BioNTech have is for a version of the shot that protects against the original strain and the BA.1 omicron subvariant. In a Phase 2/3 study testing a 30 microgram dose, the companies reported in June that this shot elicited a better immune response against the BA.1 variant compared to version of the vaccine designed for the original strain. Based in part on those results, an FDA advisory committee then voted to recommend that an omicron component be part of new booster shots.

After the committee vote, the FDA issued guidance advising all Covid-19 vaccine makers to modify their boosters to address the BA.4 and BA.5 subvariants that have become the dominant strains in the U.S. At the time, Peter Marks, director of the FDA’s Center for Biologics Evaluation and Research, said that clinical data for BA.1 would be sufficient for seeking authorization of booster shots addressing the BA.4 and BA.5 subvariants.

Pfizer and BioNTech have only preclinical data testing their booster against the BA.4 and BA.5 subvariants. In those results, the companies reported that the shot generated a strong neutralizing antibody response against four omicron subvariants, as well as the original strain. A clinical trial testing this updated vaccine in people 12 and older is on track to start by the end of August.

The proposed dosing schedule is a single booster shot for those who have completed the primary vaccination series of shots with any approved or authorized Covid-19 vaccine. The companies are also asking for authorization of a second booster dose in those age 50 and older, as well as those 12 and older with compromised immune systems.

“Having rapidly scaled up production, we are positioned to immediately begin distribution of the bivalent Omicron BA.4/BA.5 boosters, if authorized, to help protect individuals and families as we prepare for potential fall and winter surges,” Pfizer Chairman and CEO Albert Bourla said in a prepared statement.

The federal government reached a $3.2 billion agreement with Pfizer in June covering the purchase of 105 million doses of the booster shots. The government also has the option to buy up to 195 million additional doses. Last month, the government signed a $1.74 billion purchase agreement with Moderna for its bivalent booster shot. That deal covers the government purchase of 66 million doses with the option to buy up to 234 million more doses.

Pfizer and BioNTech are also seeking authorization for their booster shot in Europe. They said Monday that a conditional marketing authorization application with the European Medicines Agency is expected to be complete in coming days.

Photo by Christian Charisius – Pool, via Getty Images