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 <19 years among 504,407 ADR reports included in the JADER from 2004 to 2017. The number of AEFI reports gradually increased among children aged <10 years and was the highest in 2011 among children aged 10-19 years. The number of suspected vaccines per AEFI report increased after 2011 among children aged <10 years. The percentage of "death" and "did not recover" as AEFI outcomes reported were 4.3% and 3.7% among children aged <10 years and 0.2% and 21.1% among children aged 10-19 years, respectively. The most frequently reported vaccine-reaction pair was 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.
Keywords: adverse events following immunization; children; spontaneous reports; vaccine.