Seroprevalence Trends of Antibodies to SARS-CoV-2 in South Korea, 2021-2022: A Repeated Cross-Sectional Study.

BACKGROUND

Monitoring immunity levels nationwide and identifying disparities are important to prepare for future pandemics. However, data regarding changes in the seroprevalence of SARS-CoV-2 and disparities in consecutive epidemic waves using existing surveillance systems are limited.

METHODS

We conducted a cross-sectional serosurvey using 11,506 residual serum samples collected from the Korean National Health and Nutrition Examination Survey between January 2021 and December 2022. Antibodies to the SARS-CoV-2 spike (anti-S) protein, indicative of vaccination or past infection of SARS-CoV-2, and nucleocapsid (anti-N) protein, indicating infection, were quantified. Then, we applied post-stratification weighting through the bootstrap resampling based on the age and sex distribution of the South Korean population. We used regression models to identify any disparities in the seropositivity prevalence ratio (PR) across different epidemic waves of SARS-CoV-2 and demographics in the population.

RESULTS

We identified that the anti-S seropositivity gradually increased after the COVID-19 vaccination rollout, whereas anti-N seropositivity increased after the SARS-CoV-2 Omicron variant was introduced in Korea. Anti-S seropositivity PR was 0.12-0.76 times lower in individuals < 18 years than in elderly individuals ≥ 65 years during Waves 4-5 (July 2021 to June 2022). Anti-N seropositivity PR was 1.25-1.83 times higher in individuals less than 64 years than in elderly individuals during Waves 5-7 (January 2022 to December 2022).

CONCLUSIONS

Our findings provide insights into the dynamic changes in immunity levels among the Korean population after the COVID-19 vaccine rollout and the introduction of the Omicron variant. Identifying the disparity in seroprevalence in the study population during the pandemic by using the existing surveillance system provides helpful information to develop future pandemic preparedness plans for the population.