title: Long-Term Protection against Diphtheria in the Netherlands after 50 Years of Vaccination: Results from a Seroepidemiological Study.
abstract: OBJECTIVE
  To evaluate the National Immunisation Programme (NIP) a population-based cross-sectional seroepidemiological study was performed in the Netherlands. We assessed diphtheria antitoxin levels in the general Dutch population and in low vaccination coverage (LVC) areas where a relatively high proportion of orthodox Protestants live who decline vaccination based on religious grounds. Results were compared with a nationwide seroepidemiological study performed 11 years earlier.
  
  
  METHODS
  In 2006/2007 a national serum bank was established. Blood samples were tested for diphtheria antitoxin IgG concentrations using a multiplex immunoassay for 6383 participants from the national sample (NS) and 1518 participants from LVC municipalities. A cut-off above 0.01 international units per ml (IU/ml) was used as minimum protective level.
  
  
  RESULTS
  In the NS 91% of the population had antibody levels above 0.01 IU/ml compared to 88% in the 1995/1996 serosurvey (p<0.05). On average, 82% (vs. 78% in the 1995/1996 serosurvey, p<0.05) of individuals from the NS born before introduction of diphtheria vaccination in the NIP and 46% (vs. 37% in the 1995/1996 serosurvey, p = 0.11) of orthodox Protestants living in LVC areas had antibody levels above 0.01 IU/ml. Linear regression analysis among fully immunized individuals (six vaccinations) without evidence of revaccination indicated a continuous decline in antibodies in both serosurveys, but geometric mean antibodies remained well above 0.01 IU/ml in all age groups.
  
  
  CONCLUSIONS
  The NIP provides long-term protection against diphtheria, although antibody levels decline after vaccination. As a result of natural waning immunity, a substantial proportion of individuals born before introduction of diphtheria vaccination in the NIP lack adequate levels of diphtheria antibodies. Susceptibility due to lack of vaccination is highest among strictly orthodox Protestants. The potential risk of spread of diphtheria within the geographically clustered orthodox Protestant community after introduction in the Netherlands has not disappeared, despite national long-term high vaccination coverage.
authors: Centre for Infectious Disease Control, National Institute for Public Health and the Environment, Bilthoven, the Netherlands.
authors: E M
authors: EM
authors: Swart
authors: Centre for Infectious Disease Control, National Institute for Public Health and the Environment, Bilthoven, the Netherlands.
authors: P G M
authors: PG
authors: van Gageldonk
authors: Centre for Infectious Disease Control, National Institute for Public Health and the Environment, Bilthoven, the Netherlands.
authors: H E
authors: HE
authors: de Melker
authors: Centre for Infectious Disease Control, National Institute for Public Health and the Environment, Bilthoven, the Netherlands.
authors: F R
authors: FR
authors: van der Klis
authors: Centre for Infectious Disease Control, National Institute for Public Health and the Environment, Bilthoven, the Netherlands.
authors: G A M
authors: GA
authors: Berbers
authors: Centre for Infectious Disease Control, National Institute for Public Health and the Environment, Bilthoven, the Netherlands.
authors: L
authors: L
authors: Mollema
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D002648:Child; D002675:Child, Preschool; D003353:Corynebacterium diphtheriae / Q000276:immunology; D003430:Cross-Sectional Studies; D004165:Diphtheria / Q000453:epidemiology / Q000276:immunology / Q000382:microbiology / Q000517:prevention & control*; D004166:Diphtheria Antitoxin / Q000097:blood*; D004168:Diphtheria Toxoid / Q000008:administration & dosage* / Q000276:immunology; D005260:Female; D006801:Humans; D017589:Immunization Programs / Q000706:statistics & numerical data*; D007074:Immunoglobulin G / Q000097:blood*; D007223:Infant; D007231:Infant, Newborn; D008297:Male; D008875:Middle Aged; D009426:Netherlands / Q000453:epidemiology; D010342:Patient Acceptance of Health Care / Q000523:psychology / Q000706:statistics & numerical data; D033303:Protestantism / Q000523:psychology; D016036:Seroepidemiologic Studies; D013997:Time Factors; D014611:Vaccination / Q000523:psychology / Q000706:statistics & numerical data*
chemical_list: D004166:Diphtheria Antitoxin; D004168:Diphtheria Toxoid; D007074:Immunoglobulin G