Abstract
BACKGROUND: Previous SARS-CoV-2 infection provides some level of protection against reinfection. However, few studies have evaluated the neutralizing antibody (NAb) response after Delta variant infection and its ability to prevent reinfection with Omicron BA.5 one year later. METHODS: This prospective cohort study included 431 patients who recovered from Delta variant infection. We measured their serum NAb titers against both Delta and Omicron BA.5 using microneutralization tests. RESULTS: Over a 17-month follow-up, 17.9% of the participants were reinfected with Omicron BA.5. Younger adults (18-65 years) and individuals who did not receive booster immunization had significantly higher reinfection rates than older adults (>65 years) and those who received boosters (p < 0.05). Notably, reinfection rates were higher in post-vaccination breakthrough cases than in individuals who were naturally infected. However, booster immunization reduced reinfection rates within the breakthrough group. We found no significant association between Delta NAb levels and protection against Omicron BA.5 reinfection (p > 0.05). Cross-neutralization assays showed a 7.1-fold reduction in NAb efficacy against Omicron BA.5. CONCLUSIONS: Delta-variant infection-induced NAbs did not strongly predict protection against Omicron BA.5 reinfection. However, booster immunization effectively reduced the reinfection rate approximately one year after the initial Delta infection.