Changes in the trend and quality of adverse drug reaction reports in the Japanese Adverse Drug Event Report database and the impact of COVID-19-related reports

Objectives This study aimed to identify the impact of the coronavirus disease 2019 (COVID-19) pandemic on changes in the trend and quality of adverse drug reaction (ADR) reports in the Japanese Adverse Drug Events Report (JADER) database using the vigiGrade completeness score as an indicator. Methods A JADER dataset consisting of ADR reports from April 2004 to March 2025 was used. VigiGrade completeness scores were determined for ADR reports, and the quality of the reports was assessed as ‘well documented’ or not, depending on the score obtained. Key findings Of 969 520 ADR reports, 393 168 submitted between the fourth quarter of 2018 and the fourth quarter of 2024 were included. The number of ADR reports declined in the first quarter of 2020 but peaked in the second quarter of 2021. The proportion of ‘well-documented’ reports remained between ~20% and 30% during most quarters, but increased to ~40% in the first and second quarters of 2021, during which COVID-19 vaccine-related reports accounted for 29.0% and 39.2% of all reports, respectively. This surge in vaccine-related submissions coincided with a temporary improvement in documentation quality. Conclusions The COVID-19 pandemic and the increase in ADR reports related to COVID-19 vaccines have affected the trends and quality of reporting in the JADER database. Notably, a substantial increase in vaccine-related ADRs during mass immunization corresponded with a temporary rise in reporting quality. These findings highlight the importance of maintaining robust pharmacovigilance systems that can adapt to large-scale public health interventions and sustain data quality during future emergencies.