Timeliness of infant vaccination and factors related with delay in Flanders, Belgium

Achieving high vaccination coverage is a necessary, but not a sufficient indicator of the quality of a vaccination programme, in terms of control and prevention of childhood infectious diseases. For optimal protection of infants, timeliness of vaccination is increasingly recognized as another important target. The aim of this study was to assess the timeliness of measles-mumps-rubella (MMR) and diphtheria-tetanus-pertussis (DTP) vaccination in infants in Flanders (Belgium), and to identify predictors of vaccination delay. The timeliness was assessed using the Kaplan-Meier estimator in three consecutive vaccination coverage surveys among children aged 18-24 months, conducted in 2005, 2008 and 2012, respectively. Factors associated with delayed administration of the vaccines were identified using Cox regression analysis. Over the time period, vaccination coverage for the first dose of MMR ranged from 94.0 to 96.6% and for the third dose of DTP from 97.9 to 98.7%. However, up to 32% (for MMR1) and 95% (for DTP3) of infants received vaccine doses delayed according to the recommended schedule. Although some improvement was achieved over the last decade, further efforts are needed to reach risk groups with delays, more specifically children vaccinated outside the baby well clinics, born from a mother originating from outside the European Union, children with a higher ranking or in families with a lower income.