Work

Effect of anti-S antibody titers on newly confirmed cases of COVID-19 in Korea: a community-based cohort study (K-SEROSMART Wave 2)

Year: 2025

Type: article

Abstract: BACKGROUND: Coronavirus disease 2019 (COVID-19) continues to impact populations globally, raising concerns about immunity levels and risks to high-risk groups despite the lifting of the global health emergency in May 2023. While studies have tracked seroprevalence, few have comprehensively assessed long-term antibody persistence and COVID-19 risk, particularly regarding immunity changes due to vaccination and infection. This study aimed to estimate the population prevalence of SARS-CoV-2-specific antibodies, including anti-spike (anti-S) and anti-nucleocapsid (anti-N) antibodies, and to assess the risk of newly confirmed COVID-19 infections in Korea in December 2022. We conducted a follow-up survey and blood testing of 9,945 participants in the Korea Seroprevalence Study of Monitoring of SARS-CoV-2 Antibody Retention and Transmission (K-SEROSMART) Wave 1. METHODS: The K-SEROSMART Wave 2 study employed a staged approach through public health centers nationwide, using mobile web, telephone, and face-to-face surveys. The follow-up survey (Wave 2) was conducted between December 6 and 27, 2022, four months after the initial survey (Wave 1) conducted in August 2022. Participants self-reported sociodemographic characteristics and health status and provided blood samples for the analysis of anti-spike (anti-S) and anti-nucleocapsid (anti-N) antibodies via electrochemiluminescence immunoassay. Population prevalence estimates were weighted for demographic data. Multivariate Cox proportional hazards regression was used to assess the relationship between anti-S antibody titers from Wave 1 and new COVID-19 cases, adjusting for age and sex. RESULTS: A total of 7,528 individuals participated, yielding a follow-up rate of 74.9%. The population-adjusted prevalence rates of anti-S and anti-N antibodies were 98.5% and 70.0%, respectively. The percentage of newly confirmed COVID-19 cases was significantly higher in individuals with anti-S antibody titers below 2,000 U/mL, 2,000-3,999 U/mL, 4,000-5,999 U/mL, 6,000-7,999 U/mL, and 8,000-9,999 U/mL than in those with titers above 18,000 U/mL (hazard ratio [HR] = 9.9, 95% confidence interval [CI] = 7.2-13.5; HR = 8.1, 95% CI = 5.8-11.3; HR = 7.1, 95% CI = 5.0-10.1; HR = 4.2, 95% CI = 2.8-6.3; HR = 2.0, 95% CI = 1.2-3.3, respectively). CONCLUSIONS: This study demonstrated the feasibility of conducting a seroepidemiological cohort survey on COVID-19 using a nationally representative sample. Additionally, this study quantified anti-S antibody titer levels that are associated with reduced risk of new infections within a community.

Source: BMC Infectious Diseases

DOI: 10.1186/s12879-025-11753-1