Risk of new-onset seizures following immunization against COVID-19: a self-controlled case-series study.

Despite emerging reports of new-onset seizures (NOS) following COVID-19 vaccination, safety evidence regarding the risk of NOS after vaccination remains limited. We aimed to investigate the potential association between NOS and COVID-19 vaccination. We conducted a self-controlled case series study utilizing a nationwide database linking the COVID-19 vaccination registry and the National Health Information Database (from February 2021 to October 2022). We identified adults (≥18 years) who received COVID-19 vaccination (BNT162b2, ChAdOx1 nCoV-19, mRNA-1273, NVX-CoV2373, or Ad26.COV2.S) and had a diagnosis of NOS accompanied by prescriptions of anti-seizure drugs. The observation period was defined as 240 days following vaccination. We evaluated the risk of NOS during a risk window of 28 days after vaccination compared to the control window (the remaining observation period excluding the risk window). Incidence rate ratios (IRRs) with 95% confidence intervals (CIs) were estimated using a conditional Poisson regression model. Among 42,155,198 COVID-19 vaccine recipients, we identified 1,849 and 4,217 patients with NOS in the risk and control windows, respectively. There was no increased risk of NOS within the 28-day period following vaccination (IRR, 0.99; 95% CI, 0.94-1.05). Although results from subgroup analyses by vaccine type were largely consistent with the main findings (IRR, 0.95; 95% CI, 0.88-1.03 for BNT162b2; IRR, 0.95; 95% CI, 0.77-1.16 for ChAdOx1 nCoV-19; IRR, 1.58; 95% CI, 0.52-4.83 for Ad26.COV2.S), a marginally elevated risk was observed for mRNA-1273 (IRR, 1.21; 95% CI, 1.04-1.42). There was no evidence of an increased risk of NOS following COVID-19 vaccination. These findings can be used as safety evidence in clinical decision-making and to bolster public confidence in COVID-19 vaccines. .