Nationwide seroprevalence of antibodies to SARS-CoV-2 in asymptomatic population in South Korea: a cross-sectional study

Abstract

ObjectiveAsymptomatic active infection might be an important contributor to the COVID-19 outbreak. Serological tests can assess the extent of exposure and herd immunity to COVID-19 in general populations. This study aimed to estimate the nationwide seroprevalence of SARS-CoV-2 antibodies according to age, sex and clinical status in South Korea.Design, setting and participantsThis cross-sectional study randomly selected health examinees who underwent health check-up at 16 health promotion centres in 13 Korean cities across the country between late September and early December 2020. Residual serum samples were obtained from 4085 subjects (2014 men and 2071 women). Antibodies to SARS-CoV-2 were measured by electrochemiluminescence immunoassay using Elecsys Anti-SARS-CoV-2 (Roche Elecsys, Mannheim, Germany).Primary and secondary outcome measuresFisher’s exact test was used to compare the seroprevalence according to sex, age group and region. The relative risks of being seropositive according to the characteristics of the study subjects were analysed using logistic regression analysis.ResultsThe overall seroprevalence of anti-SARS-CoV-2 was 0.39% (95% CI=0.20% to 0.58%): 0.30% (95% CI=0.06% to 0.54%) for men and 0.48% (95% CI=0.18% to 0.78%) for women. The rate of anti-SARS-CoV-2 positivity varied significantly between different regions of Korea (p=0.003), but not with age group, sex, or the statuses of obesity, diabetes, hypertension or smoking.ConclusionsMost of the Korean population is still immunologically vulnerable to SARS-CoV-2, but the seroprevalence has increased relative to that found in studies performed prior to September 2020 in Korea.

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“…Finally, the current survey population was composed of people in which blood test was prescribed for medical reasons (e.g., chronic diseases), they could have been more careful and decreased their exposure to the virus, which resulted in an underestimation of seroprevalence so they may not reliably represent the whole Corsican population. However, there is no evidence to suggest a greater susceptibility to COVID-19 in people undergoing blood tests in clinical laboratories and several nationwide studies have employed this biological sample (“residual sera”) to describe SARS-CoV-2 circulation ( 2 , 26 , 27 ).…”

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“…Additionally, it was found that patients with obesity have higher anti‐SARS‐CoV‐2 levels than lean patients 82,84–86 (Figures 2 and 3). However, other studies showed that seroprevalence against SARS‐CoV‐2 did not differ with BMI or any biochemical parameters 78,83 …”

“…However, other studies showed that seroprevalence against SARS‐CoV‐2 did not differ with BMI or any biochemical parameters. 78 , 83 …”

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“…In Korea, since early in the pandemic, there has not been a shortage of COVID-19 tests, so even asymptomatic patients could freely be tested by PCR with contact tracing or voluntary testing. Consequently, undiagnosed COIVD-19 infections seem to be very rare according to a seroprevalence study in Korea [38]. In addition, all the COVID-19 patients stayed in residential treatment centers or hospitals until recovery or death and were treated without charge.…”