title: Risk of Pertussis in Relation to Degree of Prematurity in Children Less Than 2 Years of Age.
abstract: A few previous studies reported increased risk of pertussis in children with birth weight less than 2500 g. The risk of pertussis by degree of prematurity has not been determined in a cohort study. The vaccine effectiveness (VE) against reported pertussis in preterm infants is unknown.
  
  
  
  Data were obtained from the Medical Birth Registry of Norway (1998-2010) and linked to other national registries. In total, 713,166 children were included in our study and followed until 2 years of age. Incidence rate ratios (IRRs) and confidence intervals (CIs) were estimated with Poisson regression.
  
  
  
  We identified 999 reported cases of pertussis. We observed a higher rate of reported pertussis in preterm than in full-term infants, IRR = 1.65 (95% CI: 1.32-2.07). Compared to full-term infants, the risk of reported pertussis in infants born at gestational age (GA) 35-36, 32-34 and 23-27 weeks were higher [IRRs = 1.49 (95% CI: 1.11-2.01), 1.63 (95% CI: 1.06-2.51) and 4.49 (95% CI: 2.33-8.67), respectively]. Moreover, preterm infants had a higher rate of pertussis-related hospitalization than full-term infants [IRR = 1.99 (95% CI: 1.47-2.71)]. The VE against reported pertussis for the third dose was 88.8% (95% CI: 84.3-92.0) in full-term infants and 93.0% (95% CI: 85.8-96.5) in preterm infants.
  
  
  
  In this cohort study, preterm infants including those born at GA 35 and 36 weeks had increased risk of reported pertussis. The VE was similar in preterm and full-term infants.
authors.affiliation: From the *Department of Vaccine Preventable Diseases, and †Department of Infectious Disease Epidemiology and Modelling, Norwegian Institute of Public Health, Oslo, Norway; ‡Department of Global Public Health and Primary Care, University of Bergen, and §Department of Pediatrics, Haukeland University Hospital, Bergen, Norway; and ¶Department of Health Registries, Norwegian Institute of Public Health, Oslo, Norway.
authors.forename: Øystein Rolandsen
authors.initials: ØR
authors.lastname: Riise
authors.forename: Ida
authors.initials: I
authors.lastname: Laake
authors.forename: Didrik
authors.initials: D
authors.lastname: Vestrheim
authors.forename: Elmira
authors.initials: E
authors.lastname: Flem
authors.forename: Dag
authors.initials: D
authors.lastname: Moster
authors.forename: Marianne Adeleide
authors.initials: MA
authors.lastname: Riise Bergsaker
authors.forename: Jann
authors.initials: J
authors.lastname: Storsæter
mesh_terms: D001724:Birth Weight; D002675:Child, Preschool; D015331:Cohort Studies; D005260:Female; D005865:Gestational Age; D006760:Hospitalization / Q000706:statistics & numerical data; D006801:Humans; D007223:Infant; D007230:Infant, Low Birth Weight; D007231:Infant, Newborn; D007234:Infant, Premature / Q000276:immunology*; D008297:Male; D009664:Norway; D010567:Pertussis Vaccine / Q000008:administration & dosage*; D012042:Registries; D012306:Risk; D064166:Vaccine Potency; D014917:Whooping Cough / Q000175:diagnosis / Q000276:immunology / Q000517:prevention & control*
chemical_list: D010567:Pertussis Vaccine