Validation of the 5-year tetanus, diphtheria, pertussis and polio booster vaccination in the Danish childhood vaccination database

► Estimated TdaP-IPV under-reporting in the childhood vaccination database is 20.2%. ► Adjusted TdaP-IPV VC is 85.6% compared to 82.0% from the vaccination database. ► Majority of children with unregistered TdaP-IPV booster were vaccinated by a GP. ► Most common reasons for not receiving TdaP-IPV booster were forgetting and refusing. ► Validating data used for VC calculations is needed to obtain more precise estimates.