Safety and Immunogenicity of Monovalent Omicron KP.2-Adapted BNT162b2 COVID-19 Vaccine in Adults: Single-Arm Substudy from a Phase 2/3 Trial

Introduction: COVID-19 continues to cause substantial health burden, particularly among vulnerable populations. Vaccines remain a vital tool in preventing severe disease outcomes. As the causative pathogen, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) continues to evolve; therefore, updates may be needed to closely match COVID-19 vaccine composition to predominant circulating lineages to confer optimal protection. Methods: In this cohort from a substudy of an ongoing phase 2/3 trial, 102 healthy adults (18‒55 and > 55 years of age, n = 51 each) were vaccinated with Omicron KP.2-adapted BNT162b2. Serum neutralizing titers against Omicron KP.2, JN.1, and KP.3 were assessed before and through 1 month after vaccination. Immunogenicity in KP.2-adapted BNT162b2 recipients was compared with participants who received JN.1-adapted BNT162b2 in an earlier cohort of this substudy. Local reactions and systemic events through 7 days and adverse events (AEs) through 1 month are reported. Results: One month after vaccination, KP.2-adapted BNT162b2-elicited neutralizing titers against Omicron KP.2, JN.1, and KP.3 were numerically higher than those induced by JN.1-adapted BNT162b2. Geometric mean fold rises from before to 1 month after vaccination were numerically higher in those who received KP.2-adapted BNT162b2 compared with those who received JN.1-adapted BNT162b2 (9.4 vs. 6.8 for KP.2; 7.8 vs. 5.7 for JN.1; 9.2 vs. 7.0 for KP.3). Percentages of participants with seroresponses were numerically higher against KP.2 after KP.2-adapted BNT162b2 than JN.1-adapted BNT162b2 (75% vs. 65%) and similar against JN.1 and KP.3 for both vaccines (69% vs. 67% for JN.1; 74% vs. 73% for KP.3). Local reactions and systemic events were all mild to moderate in severity, AEs were infrequent, and no serious AEs or AEs leading to withdrawal were reported. Conclusions: Collectively, these immunogenicity, safety, and tolerability data support administration of KP.2-adapted BNT162b2 to protect against contemporaneous circulating lineages. ClinicalTrials.gov Identifier: NCT05997290.