Safety and immunogenicity of a homologous booster dose of a SARS-CoV-2 recombinant protein nanoparticle vaccine (GBP510) adjuvanted with AS03: 12 months follow-up result of an open-label, nonrandomized extension of a phase 1/2 trial

Objectives This study evaluated the safety and immunogenicity of a homologous GBP510/AS03 booster given 6-12 months after a primary two-dose series. Methods In an open-label extension of a phase 1/2 trial in Korea, healthy adults aged 19-85 years who had completed two doses received a single GBP510/AS03 booster. The primary objective was to assess safety and reactogenicity. Secondary objectives included assessment of humoral and cellular immunogenicity against the ancestral D614G strain and Omicron variants. Results Between December 2021 and January 2022, 81 participants received the booster and 56 completed 12-month follow-up. No immediate systemic reactions were reported. The most common local adverse event was injection site pain, while systemic events such as myalgia, fatigue, and chills were mostly mild to moderate. No serious adverse events related to vaccination occurred. Neutralizing antibody titres and seroconversion rates against D614G following the booster were noninferior to those observed after the primary series. Cross-neutralization responses to Omicron variants improved after boosting, and neutralizing antibody titres to early Omicron variants and the ancestral strain were sustained for up to 12 months. Conclusions A homologous GBP510/AS03 booster was well tolerated and induced robust, durable neutralizing antibody responses against SARS-CoV-2, including Omicron variant.