Active surveillance of adverse events following immunisation in children: pre, during and post COVID-19 pandemic

In Singapore, a sentinel surveillance site was established in 2009 at KK Women's and Children's Hospital (KKH) in partnership with the Health Sciences Authority to conduct active surveillance of adverse events following immunisation (AEFIs) in the paediatric population. In 2021, the surveillance was extended to COVID-19 vaccines. The aim of this study is to update the surveillance findings for the pre-COVID-19 (2013–2019), COVID-19 (2020−2022), and post-COVID-19 (2023) pandemic periods. Paediatric patients aged 0–17 years admitted between 2013 and 2023 were eligible for inclusion in this report. Daily screenings of electronic health records and monthly extraction of diagnosis codes were used to identify potential AEFIs. The data collected included demographic, clinical, laboratory and immunisation history. A multidisciplinary panel reviewed the cases. Monthly AEFI rates per 1000 vaccine doses were calculated and statistical analysis was performed to compare changes in vaccination uptake and AEFI rates over time. 326,780 out of 363,089 total hospital admissions were screened. 3429 children with suspected AEFIs were evaluated, with 2863 classified as “Possible-and-Above” following recent vaccination. The yearly rates of AEFIs with childhood vaccines were 0.26–0.33 per 1000 doses for the pre- and post-COVID-19 pandemic periods compared to 0.11–0.17 per 1000 doses during the pandemic. AEFI rates for COVID-19 vaccines were 0.77 and 0.48 per 1000 doses in 2021 and 2022, respectively. For childhood vaccines, the more common AEFIs were regional lymphadenitis following Bacillus-Calmette-Guérin vaccination, febrile seizures with measles-mumps-rubella vaccines, and afebrile seizures with 5-IN-1 and pneumococcal vaccines. For COVID-19 vaccines, the more common AEFIs included chest pain, appendicitis, seizures, and myocarditis/pericarditis. Further analysis identified increased risk of appendicitis and myocarditis/pericarditis with COVID-19 vaccines. No new safety concerns with childhood vaccines were identified. Overall, the study provides insights into the safety of vaccines in children over a decade, highlighting the importance of sentinel site surveillance.