(SLC-031) Adverse events of special interest (AESI) Following COVID-19 Vaccination in Children and Adolescents Aged 5–17 Years: A Retrospective Cohort Study in South Korea

Background: Evaluating vaccine safety in vulnerable populations, such as children and adolescents, is crucial due to their unique physiological characteristics and developmental stages, which may influence adverse event risks. However, data on the safety profile of adverse events of special interest (AESI) following COVID-19 vaccination in this population remains limited in Korea.

Objectives: To evaluate the risk of AESI according to COVID-19 vaccination status among children and adolescents in South Korea.

Methods: This study is a retrospective cohort study using linked data from the Korea Disease Control and Prevention Agency’s COVID-19 registry and the National Health Insurance Service claims database. Individuals aged 5-17 years who received at least one dose of monovalent or bivalent BNT162b2, mRNA-1273, NVX-CoV2373, or GBP510 vaccine between February 2021 and June 2024, as well as those who remained unvaccinated individuals, were included in the study. Propensity scores were calculated using a logistic regression model with sex, age, insurance type, region of residence, and income as covariates, followed by 1:1 Greedy matching. A total of 27 AESIs were evaluated, defined using the ICD-10 codes, including those specified by the Safety Platform for Emergency vACcines (SPEAC). Index date was defined as the date of the first vaccination for the vaccinated group or the matched date for the unvaccinated group. Individuals with a confirmed COVID-19 infection before the index date or with a relevant AESI diagnosis in the previous three years were excluded. All AESIs were followed from the day after the index date up to 28 days, except anaphylaxis and generalized convulsion, which were followed from day 0 to 1. Follow-up continued until the earliest occurrence of the first AESI, COVID-19 infection, death, or the end of the study period. Using conditional Poisson regression adjusted for the pediatric comorbidity index, we estimated adjusted incidence rate ratios (aIRR) and 95% confidence intervals (CI) were estimated.

Results: A total of 2,369,407 vaccinated and 3,547,102 unvaccinated individuals were identified. After matching, 250,399 participants remained in each group. The aIRR was 2.22 (95% CI, 1.40–3.53) for pulmonary embolism (PE) and 6.43 (95% CI, 2.27–18.21) for immune thrombocytopenia (ITP). No other AESIs showed statistically significant associations.

Conclusions: This study found a significant association between COVID-19 vaccination and an increased risk of PE and ITP in children and adolescents in South Korea. However, due to the rarity of these events, these findings should be interpreted with caution, and further research is needed to investigate potential causal mechanisms.