Detection of delayed vaccinations: a new approach to visualize vaccine uptake.

For the prevention of pertussis and invasive Haemophilus influenzae type b (Hib) infections, each with a peak for mortality and serious complications in the first year of life, early vaccination is important and needs adequate monitoring. In a 1999 national coverage survey the timing of uptake of these vaccines in German children was therefore assessed conventionally at defined age thresholds and with a new adaptation of the Kaplan-Meier (KM) method estimating immunization uptake over time by 1 minus the survival function s(t). Only 6% and 9% of children were vaccinated against pertussis and Hib in accordance with the national recommended primary vaccination schedule. Coverage levels for the primary vaccination course of 50% and 90% were attained for pertussis after 6.6 and 16.3 months respectively and for Hib after 7.0 and 24.3 months. These estimates were only possible with the KM method which proved useful to monitor vaccination programmes and will allow the comparison of vaccination uptake in different populations.