Research protocol of Proportion, clinical sequelae, and risk factors of SARS-CoV-2 Omicron variant reinfection in Hong Kong children: a population-level observational study

Abstract Background: The rapid spread of the SARS-CoV-2 Omicron variant has led to significant public health concerns, particularly regarding reinfection rates among children. The Omicron subvariants BA.4 and BA.5 have shown differences in infection dynamics compared to earlier strains. Understanding the proportion of reinfections, associated clinical sequelae, and risk factors influencing disease severity in this vulnerable population is critical. This study addresses these concerns by analyzing population-level data from Hong Kong children. Methods: This retrospective cohort study will utilize electronic health records from the Hospital Authority and vaccination data from the Department of Health in Hong Kong. Participants will include children aged 0-18 years with confirmed SARS-CoV-2 infections. The study will identify reinfection cases and compare clinical outcomes between initial infections and reinfections. Data analysis will involve descriptive statistics, logistic regression models, and Kaplan-Meier survival analysis to assess the risk factors and clinical outcomes associated with reinfection. Discussion: The findings from this study are expected to provide essential insights into the burden of SARS-CoV-2 reinfections among children, mainly focusing on the Omicron BA.4 and BA.5 subvariants. Health authorities can better tailor public health interventions and vaccination strategies by understanding the frequency of reinfections and their clinical impacts. This study will contribute to the global understanding of COVID-19's evolving epidemiology and help mitigate the ongoing impacts of the pandemic on children’s health. Trial registration: retrospectively registered.