One-year Antibody Durability Induced by EuCorVac-19, a Liposome-Displayed COVID-19 RBD Subunit Vaccine, in Healthy Korean Subjects

BackgroundEuCorVac-19 (ECV-19), an adjuvanted liposome-displayed receptor binding domain (RBD) COVID-19 vaccine, previously reported interim Phase 2 trial results showing induction of neutralizing antibodies 3 weeks after prime-boost immunization.MethodsTo assess immunogenicity 6 and 12 months after vaccination, participants in the Phase 2 trial (NCT04783311) were excluded who 1) withdrew, 2) reported COVID-19 infection or additional vaccination, or 3) exhibited increasing Spike antibodies (representing possible non-reported infection). Following exclusions, of 197 initial subjects, anti-Spike IgG antibodies and neutralizing antibodies were further assessed in 124 subjects at the 6-month timepoint, and 36 subjects at the 12-month timepoint.FindingsMedian anti-Spike antibody half-life was 52 days (interquartile range, IQR:42-70), in the “early” period from 3-weeks to 6-months, and 130 days (IQR:97-169) in the “late” period from 6- to 12-months. There was a negative correlation between initial antibody titer and half-life. Anti-Spike and neutralizing antibody responses were correlated. Neutralizing antibody responses showed longer half-lives; the early period had a median half-life of 120 days (IQR:81-207), and the late period had a median half-life of 214 days (IQR:140-550).InterpretationThese data establish antibody durability of ECV-19, using a framework to analyze COVID-19 vaccine-induced antibodies during periods of high infection.FundingThe South Korean Ministry of Health and Eubiologics