In the fall of 2022, the FDA issued EUAs to both Pfizer-BioNTech and Moderna for bivalent booster dose of COVID-19 mRNA vaccine, containing the original Wuhan strain and the BA.4 and BA.5 SARS-CoV-2 Omicron variant for use in all individuals six months of age and older. Clinical trials of the vaccine were not required by the FDA and no safety data is available to support the use of these experimental products.
Similarly, in September 2023, the FDA approved use of updated COVID-19 vaccines for 2023-2024 containing the SARS-CoV-2 Omicron variant XBB.1.5. The FDA did not require clinical trials of these vaccines prior to their approval and authorization.
Moderna, however, conducted a clinical trial involving 101 individuals previously vaccinated with 3 doses of the original monovalent COVID-19 vaccine and one dose of bivalent COVID-19 vaccine. In this study, fifty adult participants received a 50mcg dose of a monovalent COVID-19 vaccine containing the SARS-CoV-2 Omicron variant XBB.1.5 and fifty-one participants received a dose of a bivalent COVID-19 vaccine containing 25mcg of SARS-CoV-2 Omicron XBB.1.5 variant and 25mcg of Omicron BA.4/BA.5. According to the study, most clinical trial participants reported both localized and system adverse reactions following vaccination. Researchers, however, reported that no serious adverse events or deaths occurred among trial participants but data was limited to only 20-22 days post vaccination.
Pfizer- BioNTech Bivalent COVID-19 mRNA Vaccine Adverse Events
In January 2023, the FDA and CDC announced that they were investigating a potential link between the Pfizer-BioNTech Bivalent mRNA COVID-19 vaccine containing the original SARS-CoV-2 strain and the Omicron BA.4/BA.4 variant and ischemic stroke in persons 65 years and older. The possible safety signal, which was detected in the CDC’s Vaccine Safety Datalink (VSD), found an increased risk of stroke within the first 21 days after vaccination when compared to day 22-42.
