Analysis of re-infection cases and influencing factors post first severe COVID-19 wave in Jiangsu Province, China

Abstract

Introduction: This study aimed to assess COVID-19 re-infection rates among individuals previously infected between 2020 and November 2022, particularly during the first wave of high-intensity transmission, and to identify the risk factors associated with re-infection in Jiangsu Province, China.

Methodology: Epidemiological investigations were conducted through telephone interviews and face-to-face visits in February and March 2023. Statistical analyses included the Chi-square or Fisher`s exact test for categorical data, Student’s t-test for numerical data, Poisson regression for influencing factors, and Kaplan–Meier for cumulative re-infection risk.

Results: Among 12,910 individuals surveyed, 957 (7.4%) cases of re-infection were identified. Re-infection rates varied significantly by initial infection period: 42.5% in January–February 2020, 15.5% in July–August 2021, 6.7% in March–April 2022, and 1.1% in September–October 2022. Females and individuals aged 18–50 years were more susceptible to re-infection. A reduced risk of re-infection was observed in those who received four vaccine doses, with a relative risk of 0.25 (p = 0.019).

Conclusions: For populations prone to COVID-19 re-infections, particularly females and young adults aged 18–50 years, receiving four or more vaccine doses effectively reduces the likelihood of repeated infections. These findings emphasize the need to prioritize vaccination and protect high-risk groups in COVID-19 prevention efforts.