The present study aimed to describe the trends and characteristics of adverse events following immunization (AEFI) reporting for children in the Japanese Adverse Drug Event Report database (JADER). We used 6280 AEFI reports for children aged Haemophilus influenzae type b conjugate vaccine and pyrexia among children aged <10 years and recombinant adsorbed bivalent human papillomavirus-like particle vaccine and a loss of consciousness among children aged 10–19 years. It is necessary to consider the Weber effects to understand the trend and characteristics of AEFI reporting because pharmacovigilance activity regarding vaccination is not sufficient in Japan.
