In both age groups, 14 days following vaccination, LP.8.1-neutralizing antibody titers exceeded pre-vaccination levels, on average, by at least 4-fold. The safety profile of the vaccine was consistent with previous studies, with no new safety concerns identified. The favorable neutralizing antibody responses and consistent safety profile of the LP.8.1-adapted vaccine for individuals with higher risk and who had been previously exposed to SARS-CoV-2 provide early information for prescribers for this year's vaccination period. This study was conducted to provide additional information about immunological effects of the vaccine and is not intended to replace the post marketing commitments requested by the FDA. To date, 5 billion doses have been distributed globally of the Pfizer-BioNTech COVID-19 vaccine, which continues to demonstrate a favorable safety and efficacy profile supported by extensive real-world evidence as well as by clinical, non-clinical, pharmacovigilance, and manufacturing data.