title: Monitoring of timely and delayed vaccinations: a nation-wide registry-based study of Norwegian children aged < 2 years.
abstract: BACKGROUND
  Delayed vaccinations increase the risk for vaccine preventable diseases (VPDs). Monitoring of delayed vaccinations by using a national immunisation registry has not been studied in countries recommending a two-dose (3 and 5 months of age) primary series of e.g., pertussis vaccine. Surveillance/monitoring of all vaccinations may improve vaccination programmes functioning.
  
  
  METHODS
  We obtained information from the Norwegian immunisation registry (SYSVAK) on all programme vaccinations received at age up to 730 days in children born in 2010 (n = 63,382). Timely vaccinations were received up to 7 days after the recommended age. Vaccinations were considered delayed if they were received more than one month after the recommended age in the schedule.
  
  
  RESULTS
  In vaccinated children, timely administration of the subsequent three doses of pertussis and one dose of measles occurred in 73.8, 47.6, 53.6 and 43.5 % respectively. Delay for one or more programme vaccinations (diphtheria, tetanus, pertussis, polio, Haemophilus influenza type B, invasive pneumococcal disease, measles, mumps or rubella) was present in 28,336 (44.7 %) children. Among those who were delayed the mean duration was 139 days. The proportion of children that had vaccinations delayed differed among counties (range 37.4 %-57.8 %). Immigrant children were more frequently delayed 52.3 % vs. 43.1 %, RR 1.21 (95 % CI 1.19, 1.24). Children scheduled for vaccines in the summer holiday month (July) were more frequently delayed than others (1(st) dose pertussis vaccine 6.5 % vs. 3.9 % RR 1.65 (95 % CI 1.48, 1.85). Priming against pertussis (2(nd) dose), pneumococcal (2(nd) dose) and measles (1(st) dose) was delayed in 16.8, 18.6 and 29.3 % respectively.
  
  
  CONCLUSIONS
  Vaccinations were frequently delayed. Delayed vaccinations differed among counties and occurred more frequently during the summer vacation (July) and in the immigrant population. Monitoring improves programme surveillance and may be used on an annual basis.
authors.affiliation: Division of Infectious Disease Control, Department of Vaccines, Norwegian Institute of Public Health, P.O. Box 4404, Nydalen, NO-0403, Oslo, Norway. oeri@fhi.no.
authors.forename: Øystein Rolandsen
authors.initials: ØR
authors.lastname: Riise
authors.affiliation: Division of Infectious Disease Control, Department of Vaccines, Norwegian Institute of Public Health, P.O. Box 4404, Nydalen, NO-0403, Oslo, Norway. Ida.Laake@fhi.no.
authors.forename: Ida
authors.initials: I
authors.lastname: Laake
authors.affiliation: Division of Infectious Disease Control, Department of Vaccines, Norwegian Institute of Public Health, P.O. Box 4404, Nydalen, NO-0403, Oslo, Norway. marianne.bergsaker@fhi.no.
authors.forename: Marianne Adeleide Riise
authors.initials: MA
authors.lastname: Bergsaker
authors.affiliation: Division of Infectious Disease Control, Division Management, Norwegian Institute of Public Health, P.O. Box 4404, Nydalen, NO-0403, Oslo, Norway. hanne.noklebye@fhi.no.
authors.forename: Hanne
authors.initials: H
authors.lastname: Nøkleby
authors.affiliation: Division of Infectious Disease Control, Department of Vaccines, Norwegian Institute of Public Health, P.O. Box 4404, Nydalen, NO-0403, Oslo, Norway. inger.lise.haugen@fhi.no.
authors.forename: Inger Lise
authors.initials: IL
authors.lastname: Haugen
authors.affiliation: Division of Infectious Disease Control, Department of Vaccines, Norwegian Institute of Public Health, P.O. Box 4404, Nydalen, NO-0403, Oslo, Norway. Jann.Storsaeter@fhi.no.
authors.forename: Jann
authors.initials: J
authors.lastname: Storsæter
mesh_terms: D002675:Child, Preschool; D054242:Emigrants and Immigrants; D006801:Humans; D007115:Immunization Schedule; D007223:Infant; D009664:Norway; D012042:Registries; D013997:Time Factors; D014611:Vaccination