A survey on the situation and risk factors of secondary infection after the second wave of the Omicron COVID-19 in China

Introduction: Reinfection with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has been occurring more frequently. Healthcare workers are among the most at-risk groups due to their direct exposure to SARS-CoV-2 while providing medical care. We aimed to understand the potential factors that affect reinfection. Methodology: 1399 healthy workers at the General Hospital of Central Theater Command were enrolled for an online questionnaire from 27 June to 10 July 2023. The selected individuals were divided into the primary infection group and the secondary infection group based on the number of SARS-CoV-2 infections. Results: About 95% of the total population had been vaccinated. A higher proportion of the primary group had received 3 doses of vaccines and inactivated vaccines, than the secondary group (p < 0.001). The symptoms, duration, and severity of the majority of participants significantly decreased during secondary infection, compared to primary infection. After adjusting for factors such as gender, age, vaccine dose, and vaccine type; multiple regression analysis indicated that the patients with disease duration > 7 days or long coronavirus disease 2019 (long COVID-19) history during primary infection had a higher risk of secondary infection with Omicron (odds ratio, OR = 2.2, p < 0.001; OR = 2.4, p < 0.001). Conclusions: The patients with history of long COVID-19 or longer duration of disease after primary infection had a higher risk of Omicron reinfection. This study identified the clinical manifestations during Omicron primary and secondary infection; and the potential factors that may influence reinfection.