Safety and immunogenicity of COVID-19 vaccine ZF2001 in Chinese aged 60 years and older

Abstract

Coronavirus disease 2019 (COVID-19) is still causing ongoing human pandemic. Older adults are the population at high risk of developing severe COVID-19 or death. ZF2001, a protein subunit vaccine comprising two copies of tandem receptor-binding domain (RBD), has demonstrated safety and immunogenicity in population aged 3-17 and 18-59 after three doses of vaccination. Moreover, it has shown efficacy in the prevention of symptomatic COVID-19 after a six-month follow-up for adults beyond 18 years of age in a phase 3 trial. However, its immunogenicity in individuals 60 years of age and older has not been reported and needs further investigation. Here, we evaluated the safety and immunogenicity of ZF2001 in this older age group. All adverse events were grade 1 and 2 (11/20 participants in the 25 μg group; 12/20 participants in the 50 μg group; 4/10 participants in the placebo group). No serious adverse events were considered relevant to the investigational products. The seroconversion rate for neutralizing antibody against SARS-CoV-2 prototype live virus was approximately 95% on day 30 after the third dose, and it remained above 75% after half a year. However, those serum samples exhibited limited neutralization capabilities against the omicron BA.4/5 and XBB.1.16 pseudoviruses, highlighting the urgent need to develop next-generation COVID-19 vaccines.