Longitudinal Cohort Event Monitoring of MMR and DT-IPV Vaccination at 9 Years of Age in The Netherlands

<b>Background/Objectives</b>: The Dutch National Immunisation Programme (NIP) aims to protect children against severe infectious diseases. As with all vaccines, adverse events following immunisation (AEFIs) may occur with the use of vaccines in the NIP. Safety of the vaccines is monitored by The Netherlands Pharmacovigilance Centre Lareb. This study aimed to systematically document AEFIs following administration of the MMR and DT-IPV vaccines, which are given simultaneously at the age of 9 years. <b>Methods</b>: A cohort event monitoring (CEM) study was performed, employing a longitudinal cohort design. Parents or guardians of 9-year-olds receiving the MMR and DT-IPV vaccines completed questionnaires following vaccination to report the presence or absence of AEFI. <b>Results</b>: AEFIs were reported for more than 73% of children given an MMR and DT-IPV vaccination. The great majority of the reported reactions were non-serious and self-limiting and consistent with those listed in the official product information for the MMR and DT-IPV vaccines. Injection site reactions were significantly more frequent at the site of the DT-IPV vaccination than the MMR vaccination. AEFIs were mostly perceived as little or moderately burdensome. <b>Conclusions</b>: AEFIs very frequently occurred after MMR and DT-IPV vaccination. This study provides further insight into the timing and duration of AEFIs after MMR and DT-IPV vaccination. In addition, detailed insight into the adverse event profile of these vaccines is provided, which helps to set realistic expectations for children and their parents or caretakers who follow the NIP and helps health professionals in their communication regarding AEFIs.