Washington, DC—Pharmacists have been busy administering Pfizer-BioNTech COVID-19 booster shots to Americans aged 65 years and older, as well as younger adults who are at high risk for severe COVID-19 or have frequent institutional or occupational exposure to SARS-CoV-2.

Now, millions more vaccine recipients become eligible with the expansion of booster recommendations for patients in the same categories who received the Moderna and Janssen (J&J) COVID-19 vaccines.

The FDA’s amendment of the emergency-use authorizations (EUAs) for those products comes with a dose of complexity, however. In the case of the Moderna vaccine, the booster dose is not the same as the earlier vaccines, but a half-dose shot. In addition, the FDA has now paved the way for the use of each of the available COVID-19 vaccines as a heterologous—essentially a “mix and match,”—booster dose for patients who have completed their primary vaccinations with a different available COVID-19 vaccine.

On the other hand, public-health agencies did not expand the EUAs for the booster vaccines to everyone in the United States eligible to be immunized, as promoted by the Biden administration, with skepticism expressed on whether that really was necessary.

In late October, the FDA authorized the use of a single half-dose booster of the Moderna COVID-19 vaccine, to be administered at least 6 months after completion of the primary series, and a full booster dose of the J&J COVID-19 vaccine, at least 2 months after completion of the single-dose primary regimen, in patients aged 18 years and older.

The agency also clarified that a single booster dose of the Pfizer-BioNTech COVID-19 vaccine may be administered at least 6 months after completion of the primary series to individuals aged 18 to 64 years with frequent institutional or occupational exposure to SARS-CoV-2.

“The amendments to the emergency use authorizations to include a single booster dose in eligible populations are based on the available data and information and follows the input from the members of our advisory committee who were supportive of the use of a booster dose of these vaccines in eligible populations,” said Peter Marks, MD, PhD,  director of the FDA’s Center for Biologics Evaluation and Research.

“We are also taking action today to include the use of mix and match boosters to address this public health need. We will work to accrue additional data as quickly as possible to further assess the benefits and risks of the use of booster doses in additional populations and plan to update the healthcare community and public with our determination in the coming weeks.”

In expanding the EUA for the Moderna vaccine, the FDA analyzed immune-response data from 149 participants aged 18 years and older from the original clinical studies who received a booster dose at least 6 months after their second dose and compared it with the immune responses of 1,055 study participants after completing their two-dose series. The FDA reported that a heightened response was documented 29 days after receipt of the booster.

“This emergency use authorization is supported by robust clinical evidence that a 50 µg booster dose induces a strong immune response against COVID-19. We thank the FDA for their review and for this EUA including for those people who have completed a primary vaccination with a different COVID-19 vaccine,” said Stéphane Bancel, chief executive officer of Moderna. “We believe that mRNA vaccines are uniquely positioned to adapt to the evolving epidemiology of SARS-CoV-2. We’re grateful for the opportunity to provide individuals with another layer of protection.”

In a press release, Moderna noted that neutralizing antibody titers had waned prior to boosting, especially against variants of concern, such as delta, after about 6 months. “Notably, a booster dose of mRNA-1273 at the 50-µg dose level boosted neutralizing titers significantly above the Phase 3 benchmark,” the company added.

The authorization for emergency use of the single booster dose of the J&J vaccine is based on the FDA’s evaluation of immune-response data in 39 participants in a clinical trial, including 24 participants aged 18 to 55 years and 15 participants aged 65 years and older.  “The study participants received a booster dose approximately 2 months after their first dose, and the results demonstrated a booster response,” the FDA reported.

In authorizing the use of heterologous doses for FDA-authorized or -approved COVID-19 vaccines, the agency determined that the known and potential benefits of the use of a single heterologous booster dose outweigh the known and potential risks of their use in eligible populations.

Pharmacists should know that the eligible populations for a heterologous dose are the same as for any booster dose. Upon request, any adult may receive a booster dose of any of the three vaccines at least 2 months after the J&J initial series or 6 months after the Pfizer or Moderna series.

A single booster dose of any of the available COVID-19 vaccines may be administered as a heterologous booster dose following completion of primary vaccination with a different available COVID-19 vaccine. The eligible population(s) and dosing interval for a heterologous booster dose are the same as those authorized for a booster dose of the vaccine used for primary vaccination.

The content contained in this article is for informational purposes only. The content is not intended to be a substitute for professional advice. Reliance on any information provided in this article is solely at your own risk.