By Marie Rosenthal, MS

The FDA amended the emergency use authorization (EUA) for the Pfizer-BioNTech COVID-19 messenger RNA (mRNA) vaccine to enable a booster dose to be administered at least six months after completion of the primary series in people:

  • 65 years of age and older;
  • 18 through 64 years of age at high risk for severe COVID-19; and
  • 18 through 64 years of age whose frequent institutional or occupational exposure to SARS-CoV-2 puts them at high risk for serious complications of COVID-19 including severe COVID-19. This includes health care workers, first responders, and teachers and day care staff.

The amendment only applies to the Pfizer-BioNTech mRNA vaccine. The FDA-authorized Pfizer-BioNTech COVID-19 vaccine is the same formulation as the branded Comirnaty vaccine, and the vaccines may be used interchangeably, according to the FDA.

A third dose of the vaccine was previously authorized for individuals at least 12 years of age who have undergone a solid-organ transplant, or who are diagnosed with conditions that are considered to have an equivalent level of immunocompromise. This authorization of a third dose for immunocompromised individuals—administered at least 28 days after the second dose—is distinct from the booster dose authorized on Sept. 22. The third dose for immunocompromised individuals is meant to address the fact that these patients do not develop a strong immune response after two doses of the vaccine. 

In contrast, the booster dose authorization refers to an additional dose of the vaccine that is given because the immunity from the primary series is waning.

“After considering the totality of the available scientific evidence and the deliberations of our advisory committee of independent, external experts, the FDA amended the EUA for the Pfizer-BioNTech COVID-19 Vaccine to allow for a booster dose in certain populations such as health care workers, teachers and day care staff, grocery workers and those in homeless shelters or prisons, among others,” said acting FDA Commissioner Janet Woodcock, MD. 

The mRNA vaccine was approved by the FDA on Aug. 23, for the prevention of COVID-19 caused by SARS-CoV-2 in individuals 16 years of age and older. On Aug. 25, 2021, the FDA received a supplemental biologics license application seeking approval of the booster for those 16 and older.

The FDA convened a public meeting of its Vaccines and Related Biological Products Advisory Committee (VRBPAC), which recommended against the broader booster that Pfizer-BioNTech wanted, and instead recommended the vaccine schedule that was authorized by the FDA.

“The FDA considered the data that the vaccine manufacturer submitted, information presented at the VRBPAC meeting, and the committee’s discussion, and has determined that based on the totality of the available scientific evidence, a booster dose of Pfizer-BioNTech COVID-19 Vaccine may be effective in preventing COVID-19 and that the known and potential benefits of a booster dose outweigh the known and potential risks in the populations that the FDA is authorizing for use,” the agency said in a statement.

To support the authorization for a booster, the FDA analyzed safety and immune response data from a subset of participants from the original clinical trial of the Pfizer-BioNTech COVID-19 vaccine. In addition, consideration was given to real-world data on the vaccine’s efficacy over a sustained period provided by both U.S. and international sources, including the CDC, the United Kingdom and Israel.

The immune responses of approximately 200 participants 18 through 55 years of age who received a single booster dose approximately six months after their second dose were assessed. The antibody response against SARS-CoV-2 virus one month after a booster dose of the vaccine compared with the response one month after the two-dose primary series in the same individuals demonstrated a booster response.

A booster dose of the vaccine elicited significantly higher neutralizing antibody titers against the initial SARS-CoV-2 virus (wild type), as well as the beta and delta variants, when compared with the levels observed after the two-dose primary series. The reactogenicity profile within seven days after the booster dose was typically mild to moderate, and the frequency of reactions was similar to or lower than after dose 2. The adverse event profile was generally consistent with other clinical safety data for the vaccine.

Safety was evaluated in 306 participants 18 through 55 years of age and 12 participants 65 years of age and older who were followed for an average of over two months. The most commonly reported side effects by the clinical trial participants who received the booster dose of the vaccine were pain, redness and swelling at the injection site, as well as fatigue, headache, muscle or joint pain, and chills.

Of note, swollen lymph nodes in the underarm were observed more frequently following the booster dose than after the primary two-dose series.

“We’re grateful for the advice of the doctors, scientists and leading vaccine experts on our advisory committee and the important role they have played in ensuring transparent discussions about COVID-19 vaccines. We appreciate the robust discussion, including the vote regarding individuals over 65 years of age and individuals at high risk for severe disease, as well as the committee’s views regarding the use of a booster dose for those with institutional or occupational exposure to SARS-CoV-2,” said Peter Marks, MD, PhD, the director of the FDA’s Center for Biologics Evaluation and Research. “The FDA considered the committee’s input and conducted its own thorough review of the submitted data to reach today’s decision. We will continue to analyze data submitted to the FDA pertaining to the use of booster doses of COVID-19 vaccines and we will make further decisions as appropriate based on the data.”

The CDC’s Advisory Committee on Immunization Practices will meet to discuss a potential recommendation for the use and rollout of boosters to Americans.

The companies said they will have no trouble providing enough vaccine for the primary and booster doses.

—From company and FDA press materials