Efficacy, immunogenicity, and safety of a monovalent mRNA vaccine, ABO1020, in adults: A randomized, double-blind, placebo-controlled, phase 3 trial

Background: ABO1020 is a monovalent COVID-19 mRNA vaccine. Results from a phase 1 trial showed ABO1020 was safe and well tolerated, and phase 3 trials to evaluate the efficacy, immunogenicity, and safety of ABO1020 in healthy adults are urgently needed. Methods: We conducted a multinational, randomized, placebo-controlled, double-blind, phase 3 trial among healthy adults (ClinicalTrials.gov: NCT05636319). Participants were randomly assigned (1:1) to receive either 2 doses of ABO1020 (15 μg per dose) or placebo, administered 28 days apart. The primary endpoint was the vaccine efficacy in preventing symptomatic COVID-19 cases that occurred at least 14 days post-full vaccination. The second endpoint included the neutralizing antibody titers against Omicron BA.5 and XBB and safety assessments. Findings: A total of 14,138 participants were randomly assigned to receive either vaccine or placebo (7,069 participants in each group). A total of 366 symptomatic COVID-19 cases were confirmed 14 days after the second dose among 93 participants in the ABO1020 group and 273 participants in the placebo group, yielding a vaccine efficacy of 66.18% (95% confidence interval: 57.21–73.27, p < 0.0001). A single dose or two doses of ABO1020 elicited potent neutralizing antibodies against both BA.5 and XBB.1.5. The safety profile of ABO1020 was characterized by transient, mild-to-moderate fever, pain at the injection site, and headache. Conclusion: ABO1020 was well tolerated and conferred 66.18% protection against symptomatic COVID-19 in adults. Funding: National Key Research and Development Project of China, Innovation Fund for Medical Sciences from the CAMS, National Natural Science Foundation of China.