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Background: It is recommended that preterm (PT) and low birth weight infants be vaccinated according to standard guidelines. We studied the timeliness of the first diphtheria, tetanus, acellular pertussis and inactivated polio vaccination in the Netherlands, by gestational age (GA) and birth weight (BW)., Methods: We included all vaccinated children born during 2006-2010. Data from the national immunization register were used to determine the vaccination age and the proportion of timely vaccinated infants (<70 days). Results were compared between groups based on GA (extreme PT: <32, PT: 32-36, full term (FT): ≥37 weeks) and BW. Characteristics associated with the timeliness of vaccination were studied by Cox regression analyses., Results: The median vaccination age was lower with a higher GA/BW. The proportion of timely vaccinated infants was 66% for extreme PT, 76% for PT and 82% for FT infants. Similar results were seen by BW. Overall, the proportion of timely vaccinated infants increased from 2006 (77%) until 2010 (85%) and there were regional differences and differences by ethnicity. In extreme PT and PT infants, living in a very highly urbanized municipality and being light for GA were associated with less timely vaccination. Being vaccinated in a hospital was associated with a timelier vaccination in extreme PT infants. However, the reverse was seen for PT infants., Conclusions: In the Netherlands, PT and low birth weight infants were less often timely vaccinated than FT infants and were, therefore, at increased risk of vaccine-preventable infections. In FT infants, the timeliness of vaccination is better but could also be optimized.

The Netherlands vaccination schedule has been advanced by 1 month. The reporting rate of collapse or hypotonic-hyporesponsive episode increased from 5.2 [95% confidence interval (CI): 4.8-5.7] to 8.5 (95% CI: 8.0-9.1) and from 1.2 (95% CI: 1.0-1.4) to 2.5 (95% CI: 2.2-2.8) per 10,000 first and second doses, respectively. At 3 months of age it fell from 5.2 to 2.5. This suggests some protection by the first dose. Different mediators in primary and secondary immune response may play a role.