title: Duration of pertussis immunity after DTaP immunization: a meta-analysis.
abstract: OBJECTIVE
  Pertussis incidence is increasing, possibly due to the introduction of acellular vaccines, which may have decreased the durability of immune response. We sought to evaluate and compare the duration of protective immunity conferred by a childhood immunization series with 3 or 5 doses of diphtheria-tetanus-acellular pertussis (DTaP).
  
  
  METHODS
  We searched Medline and Embase for articles published before October 10, 2013. Included studies contained a measure of long-term immunity to pertussis after 3 or 5 doses of DTaP. Twelve articles were eligible for inclusion; 11 of these were included in the meta-analysis. We assessed study quality and used meta-regression models to evaluate the relationship between the odds of pertussis and time since last dose of DTaP and to estimate the probability of vaccine failure through time.
  
  
  RESULTS
  We found no significant difference between the annual odds of pertussis for the 3- versus 5-dose DTaP regimens. For every additional year after the last dose of DTaP, the odds of pertussis increased by 1.33 times (95% confidence interval: 1.23-1.43). Assuming 85% vaccine efficacy, we estimated that 10% of children vaccinated with DTaP would be immune to pertussis 8.5 years after the last dose. Limitations included the statistical model extrapolated from data and the different study designs included, most of which were observational study designs.
  
  
  CONCLUSIONS
  Although acellular pertussis vaccines are considered safer, the adoption of these vaccines may necessitate earlier booster vaccination and repeated boosting strategies to achieve necessary "herd effects" to control the spread of pertussis.
authors.affiliation: Division of Epidemiology, Dalla Lana School of Public Health, University of Toronto, Toronto, Canada ashleigh.mcgirr@mail.utoronto.ca.
authors.forename: Ashleigh
authors.initials: A
authors.lastname: McGirr
authors.affiliation: Division of Epidemiology, Dalla Lana School of Public Health, University of Toronto, Toronto, Canada.
authors.forename: David N
authors.initials: DN
authors.lastname: Fisman
mesh_terms: D000907:Antibodies, Bacterial / Q000097:blood*; D001886:Bordetella pertussis / Q000276:immunology*; D002648:Child; D002675:Child, Preschool; D015721:Diphtheria-Tetanus-Pertussis Vaccine / Q000276:immunology*; D005500:Follow-Up Studies; D006801:Humans; D007108:Immune Tolerance / Q000276:immunology; D007115:Immunization Schedule; D007117:Immunization, Secondary; D007223:Infant; D064166:Vaccine Potency; D022282:Vaccines, Acellular / Q000276:immunology; D014917:Whooping Cough / Q000276:immunology*
chemical_list: D000907:Antibodies, Bacterial; D015721:Diphtheria-Tetanus-Pertussis Vaccine; D022282:Vaccines, Acellular
keywords: DTaP; pertussis; vaccines; waning immunity; whooping cough