Adverse events following Measles-Mumps-Rubella and varicella immunization: A safety profile analysis and comparison of different vaccination schedules based on the Italian Pharmacovigilance Network in the Veneto Region

Objective The vaccines for measles, mumps, rubella and varicella (MMR and V) are mandatory in Italy since 2017. Two different vaccination strategies are suggested for the first dose: either the trivalent MMR and a separate V vaccine or the tetravalent MMRV vaccine. Our aim is to compare the safety profile of MMRV and MMR-V vaccines through the passive adverse event reporting system in the Veneto region and to perform a case-by-case review of a few conditions of interest (febrile and afebrile seizures, ataxia, encephalitis, Guillain-Barré Syndrome, thrombocytopenia, neutropenia and Henoch-Schönlein Purpura). Age and sex differences were also explored. Methods We identified all reports following MMRV or MMR-V vaccination in the Veneto Region and received into the National Pharmacovigilance Network between 2007 and April 30, 2022. Results 9,510 reports were retrieved, of which 5,662 (59.5 %) related to MMRV and 3,848 (40.5 %) to MMR-V. No safety signals were detected supporting the evidence that MMRV and MMR-V vaccinations have a good safety profile. Reporting rate (RR) for serious events between 2007 and 2022 resulted 13.67 per 10,000 administered doses for MMRV and 10.90 for MMR-V. Conclusion Passive surveillance data show a significant higher rate of serious events for males 0–2 years old, both overall and stratified per vaccination strategy. Further studies are needed to confirm this observation. The analyses suggest that retrieved differences does not have a significant impact on overall safety of both formulations.