# Tracking the evolution of serum antibody levels and influencing factors post-SARS-CoV-2 infection among community residents in Fuzhou City

## TL;DR

This study tracks how antibody levels in Fuzhou residents change over time after SARS-CoV-2 infection and identifies factors that influence these levels.

## Contribution

The study provides new insights into the long-term antibody dynamics and associated risk/protective factors in a community-based population post-COVID-19.

## Key findings

- Age, surgery history, smoking, and drinking were risk factors for lower antibody levels.
- Typical symptoms and prolonged symptoms after infection were protective factors for higher antibody levels.
- IgG antibody levels generally decreased over 3, 6, and 9 months post-infection.

## Abstract

To track the level of serum antibodies in Fuzhou residents and analyze the possible influencing factors of serum antibodies, so as to provide a scientific basis for the adjustment of population immunity and prevention and control strategies.

Residents in the Fuzhou community who had symptoms of covid-19 infection or who had tested positive for nucleic acid or antigen since December 2022 were selected for the questionnaire survey and their sera were collected to analyze the trend of antibody changes, the antibody level was divided into high antibody group and low antibody group according to the literature data. The possible influencing factors of serum antibody level was analyzed by multivariate logistic regression model.

A total of 2,521 Fuzhou residents were adopted in the study, including 223 in the high antibody group and 194 in the low antibody group. A univariate analysis showed that, there were significant differences in age (Z=-4.028, P<0.00), occupation (χ2 = 18.591, P=0.005), typical symptoms after the first infection (χ2 = 9.784, P=0.002), history of surgery (χ2 = 29.542, P<0.001), symptoms lasting more than 2 weeks after the first infection (χ2 = 4.887, P=0.027), smoking (χ2 = 18.524, P<0.001) and drinking (χ2 = 19.578, P<0.001) between the high antibody group and the low antibody group. Multivariate regression models show that, age (OR= 1.011, 95%CI: 1.002~1.020, P=0.017), history of surgery (OR=4.956,95%CI: 2.606~9.423, P<0.001),smoking (OR=2.089, 95%CI: 1.002~4.355, P=0.049), drinking (OR=2.214, 95%CI: 1.066~4.600, P=0.033) were the risk factors affecting antibody level. Typical symptoms after the first infection (OR=0.224, 95%CI: 0.086~0.579, P=0.002) and symptoms lasting more than 2 weeks after the first infection (OR=0.432, 95%CI: 0.258~0.723, P=0.001) were protective factors. By observing the trend of antibody changes in 3, 6 and 9 months, we found that the level of IgG antibody showed a decreasing trend.

The high level of protection was more likely to occur in young adults, people without operation history, people without smoking history, people without drinking history, people with typical symptoms after the first infection and symptoms lasting more than 2 weeks after the first infection. The level of IgG antibody was decreased in general, so it is necessary to strengthen immunization.