Severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) variants have caused multiple waves of infection globally. This phase 2/3 study evaluated the safety and immunogenicity of the bivalent vaccine candidate mRNA-1273.211 (equal mRNA amounts of ancestral SARS-CoV-2 and Beta variant spike proteins) as 50-µg (n=300) and 100-µg (n=595) first booster doses approximately 8.8-9.8 months after the mRNA-1273 primary series. The mRNA-1273.211 booster (50 and 100-µg) elicited higher neutralizing antibody responses against the ancestral SARS-CoV-2 and the Beta variant than that after the second mRNA‑1273 dose. Antibody responses after the 50-µg mRNA-1273.211 booster dose were also higher than that after a 50-µg mRNA-1273 booster dose for the ancestral SARS-CoV-2, Beta, Omicron and Delta variants (28 days after the booster dose) and for the ancestral SARS-CoV-2, Beta and Omicron (180 days after the booster dose), and the immunogenicity objectives were met. The safety and reactogenicity profile of the mRNA-1273.211 booster (50-µg) was comparable to mRNA-1273 (50-µg). These results indicate that bivalent booster vaccines can induce potent and durable antibody responses providing a new tool in response to emerging variants.
Trial registration: https://www.clinicaltrials.gov NCT04927065