Pfizer Inc and BioNTech SE announced the initiation of a supplemental Biologics License Application (sBLA) to the U.S. Food and Drug Administration (FDA) for the approval of a booster (third) dose of Comirnaty (Covid-19 vaccine, mRNA) to prevent Covid-19 in individuals 16 years of age and older. The companies intend to complete the submission of the sBLA by the end of this week.

The sBLA includes data from a Phase 3 clinical trial of 306 participants 18-55 years of age who received a booster (third) dose of Comirnaty between 4.8 and 8 months after completing the two-dose primary regimen, with a median follow-up time of 2.6 months post-booster. The booster (third) dose of Comirnaty elicited robust neutralizing antibodies to the wild-type strain in participants who were without evidence of SARS-CoV-2 infection through one-month post-dose-three. SARS-CoV-2 50% neutralizing titers after the third dose was 3.3 times the titers after the second dose. The post-dose-three neutralizing titers met the prespecified 1.5-fold non-inferiority criterion for success and were statistically superior. Moreover, 99.5% of participants had a four-fold response after the third dose, compared to 98.0% after the second dose. The titers after dose three met the pre-specified 10% non-inferiority margin for the difference in the four-fold seroresponse rates.

The reactogenicity profile within seven days after the booster (third) dose was typically mild to moderate. The most common events included injection site pain, fatigue, headache, muscle and joint pain, and chills. The frequency of any severe systemic event after the booster dose was low. The frequency of reactogenicity was similar to or better than after dose two of the primary series. The adverse event profile was generally consistent with other clinical data for Comirnaty

Pfizer and BioNTech intend to submit these data to a peer-reviewed journal, as well as file these data with the European Medicines Agency (EMA) and other regulatory authorities around the world in the coming weeks.

A third dose of the Pfizer-BioNTech vaccine is not currently authorized for broad use in the U.S. However, under the current amended Emergency Use Authorization, a third dose was authorized on August 12 for administration to individuals at least 12 years of age who have undergone solid organ transplantation, or who are diagnosed with conditions that are considered to have an equivalent level of immunocompromise.