Seroepidemiology of SARS-CoV-2 antibody and infection rate estimation following a high-intensity epidemic of COVID-19 in Guangdong Province, China: A large population cross-sectional investigation (Preprint)

Abstract

Background: Along with the epidemic response policy adjustment in China, a surge in COVID-19 infection occurred between December 2022 and January 2023. However, the exact proportion of individuals infected during this period remains uncertain.

Methods: A population-level seroepidemiology study was conducted from February to April 2023 in Guangdong Province. The questionnaire and venous blood samples were collected from participants and IgG antibodies against SARS-CoV-2 in serum samples were tested. The chi-square test was used to analyze differences in IgG seroprevalence among participants with different characteristics, and multivariate linear regression was performed to examine the factors affecting IgG levels. Based on a pre-survey cutoff for IgG levels, infection rates (%) for the population were estimated by characteristics.

Results: Among the total of 10,747 participants, 10,368 (96.47%, 95%CI: 96.12%-96.82%) were seropositive for SARS-CoV-2 IgG, and the median IgG was 82 (IQR:47-108) S/CO. Seroprevalence and IgG level was lower in the young, the elderly, and participants with chronic diseases. Multiple linear regression analysis revealed significant associations between IgG level and age group, gender, self-reported infection, and latest vaccination time. The infection rate of SARS-CoV-2 in the whole population in Guangdong Province was estimated to be 85.53% following the COVID-19 high-intensity epidemic, corresponding to 107.8 million population were infected.

Conclusions: The seropositive for SARS-CoV-2 IgG and the estimated natural infection rate of SARS-CoV-2 in this outbreak in Guangdong province was at a relatively high level. The young and the elderly are vulnerable populations that need to be focused on and protected.