A total of 4613 participants in the study completed the telephone survey. Coronavirus reinfection could not be determined because 40 participants could not recollect whether they had ever tested for coronavirus nucleic acid and antigen or experienced symptoms consistent with SARS-CoV-2 infection since December 2022. Consequently, 4573 participants in total were included in the analysis, consisting of 2390 males and 2183 females ranging in age from 4 months to 96 years old. 90.1% of the participants had received the complete vaccination against SARS-CoV-19, and 55.7% of the participants had already received a booster vaccination. 1940 individuals were primary infected with Delta variants, while 2633 individuals were primary infected with Omicron variants, and the distributions of sex and age were significant different between the primary Delta-infected and Omicron-infected participants (χ2 = 4.674, P = 0.031 and χ2 = 43.595, P < 0.001, respectively). The demographic and characteristics of 4573 participants are presented in Table 1. Overall, 546 SARS-CoV-2 reinfections were identified, with a pooled reinfection rate of 11.94% (95% CI: 11.03%, 12.91%). The majority of reinfections peaked in December 15–22, 2022 (Fig. 1).
Specifically, categorized by the primary infected variant, the reinfection rate for Delta variants was 25.10% (95% CI: 23.22%, 27.08%) 11–12 months after the primary infection, and for Omicron variants it was 5.92% (95% CI: 4.07%, 8.54%), 1.96% (95% CI: 1.18%, 3.27%), and 1.28% (95% CI: 0.82%, 1.99%) 7–9 months, 4–5 months, and 2–3 months after the first infection, respectively. There was a significantly increased reinfection rate though time (χ2trends = 495.21, P < 0.001).
All of the 546 reinfected individuals, 73 cases were asymptomatic, and 2 cases had a history of hospitalization during their second infection. Clinical symptoms during both COVID-19 episodes were available in 470 cases, and the most frequently reported symptoms were fever, cough, and sore throat. We then compared the differences of the various symptoms.in two episodes of infections (Table. 2). With the notable exception of fever, which was significantly less common during the second episode as compared to the first (χ2 = 11.79, P = 0.001), the asymptomatic rate was similar and the prevalence of various symptoms for the group of individuals primary infected by Omicron variants did not significantly alter between two episodes of infection. Ageusia, anosmia, and asymptomatic were considerably less common in the group of primary infected by Delta variants during the second episode than they were during the first episode.
In the multivariate analysis of reinfection-related covariates (Table 3), for those who were primary infected by Delta variants, we discovered that age (OR = 2.045, 95%CI: 1.401, 2.985) and sex (OR = 1.290, 95%CI: 1.048, 1.589) were associated with reinfection. Comparing to people over 60, adults between ages of 18 and 38 was higher risk of reinfection. However, the odds ratio (OR = 6.927, 95%CI: 3.143, 15.265) for people who were primary infected by Omicron variants revealed that being a medical worker posed a significant danger for reinfection. The logistic regression showed no evidence of a significant association between vaccination history, the time interval since last vaccination or comorbidities and reinfection.