An active surveillance study of adverse events following to Japanese encephalitis inactivated vaccine (JE-I) in Jiangsu Province, China, 2024-2025.

Abstract

Objective: To evaluate the safety of the Japanese Encephalitis Inactivated Vaccine (JE-I) through an active surveillance in Jiangsu Province, China.

Research design and methods: Active follow-up was conducted among children vaccinated with JE-I from 1 January 2024, to 31 March 2025, and systematically document the occurrence of adverse events following immunization (AEFI).

Results: A total of 274 AEFI cases were identified, yielding an overall incidence rate of 111.34 per 10,000 doses. Incidence was significantly higher after the first dose than subsequent doses (χ2 = 315.849, p < 0.001).Co-administered with other vaccines was associated with a higher AEFI incidence than JE-I alone (χ2 = 21.307, p < 0.001). Sequential vaccination demonstrated superior safety than a full JE-I course (χ2 = 18.028, p < 0.001).Most cases (84.31%) developed symptoms within one day post-vaccination. Fever was the most common symptom (92.33%). Symptoms were generally mild and transient, resolving without or with minimal intervention. Sixteen children experienced two AEFI episodes, with no aggravation in the second.

Conclusion: JE-I AEFI incidence in Jiangsu was relatively low, predominantly common reactions. No serious adverse reactions were reported, indicating a favorable safety profile.

Clinical trial registration: www.clinicaltrials.gov identifier is NCT06372665.