title: Effectiveness of maternal pertussis vaccination in England: an observational study.
abstract: BACKGROUND
  In October, 2012, a pertussis vaccination programme for pregnant women was introduced in response to an outbreak across England. We aimed to assess the vaccine effectiveness and the overall effect of the vaccine programme in preventing pertussis in infants.
  
  
  METHODS
  We undertook an analysis of laboratory-confirmed cases and hospital admissions for pertussis in infants between Jan 1, 2008, and Sept 30, 2013, using data submitted to Public Health England as part of its enhanced surveillance of pertussis in England, to investigate the effect of the vaccination programme. We calculated vaccine effectiveness by comparing vaccination status for mothers in confirmed cases with estimates of vaccine coverage for the national population of pregnant women, based on data from the Clinical Practice Research Datalink.
  
  
  RESULTS
  The monthly total of confirmed cases peaked in October, 2012 (1565 cases), and subsequently fell across all age groups. For the first 9 months of 2013 compared with the same period in 2012, the greatest proportionate fall in confirmed cases (328 cases in 2012 vs 72 cases in 2013, -78%, 95% CI -72 to -83) and in hospitalisation admissions (440 admissions in 2012 vs 140 admissions in 2013, -68%, -61 to -74) occurred in infants younger than 3 months, although the incidence remained highest in this age group. Infants younger than 3 months were also the only age group in which there were fewer cases in 2013 than in 2011 (118 cases in 2011 vs 72 cases in 2013), before the resurgence. 26?684 women included in the Clinical Practice Research Datalink had a livebirth between Oct 1, 2012 and Sept 3, 2013; the average vaccine coverage before delivery based on this cohort was 64%. Vaccine effectiveness based on 82 confirmed cases in infants born from Oct 1, 2012, and younger than 3 months at onset was 91% (95% CI 84 to 95). Vaccine effectiveness was 90% (95% CI 82 to 95) when the analysis was restricted to cases in children younger than 2 months.
  
  
  CONCLUSIONS
  Our assessment of the programme of pertussis vaccination in pregnancy in England is consistent with high vaccine effectiveness. This effectiveness probably results from protection of infants by both passive antibodies and reduced maternal exposure, and will provide valuable information to international policy makers.
  
  
  BACKGROUND
  Public Health England.
authors.affiliation: Immunisation, Hepatitis and Blood Safety Department, Public Health England, London, UK.
authors.forename: Gayatri
authors.initials: G
authors.lastname: Amirthalingam
authors.affiliation: Statistics, Modelling and Economics Department, Public Health England, London, UK.
authors.forename: Nick
authors.initials: N
authors.lastname: Andrews
authors.affiliation: Immunisation, Hepatitis and Blood Safety Department, Public Health England, London, UK. Electronic address: helen.campbell@phe.gov.uk.
authors.forename: Helen
authors.initials: H
authors.lastname: Campbell
authors.affiliation: Immunisation, Hepatitis and Blood Safety Department, Public Health England, London, UK.
authors.forename: Sonia
authors.initials: S
authors.lastname: Ribeiro
authors.affiliation: Immunisation, Hepatitis and Blood Safety Department, Public Health England, London, UK.
authors.forename: Edna
authors.initials: E
authors.lastname: Kara
authors.affiliation: Vigilance and Risk Management of Medicines, Medicines and Healthcare Products Regulatory Agency, London, UK.
authors.forename: Katherine
authors.initials: K
authors.lastname: Donegan
authors.affiliation: Respiratory and Vaccine Preventable Bacterial Reference Unit, Public Health England, London, UK.
authors.forename: Norman K
authors.initials: NK
authors.lastname: Fry
authors.affiliation: Immunisation, Hepatitis and Blood Safety Department, Public Health England, London, UK.
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Miller
authors.affiliation: Immunisation, Hepatitis and Blood Safety Department, Public Health England, London, UK.
authors.forename: Mary
authors.initials: M
authors.lastname: Ramsay
mesh_terms: D000328:Adult; D004739:England; D005260:Female; D006760:Hospitalization / Q000706:statistics & numerical data; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D018445:Infectious Disease Transmission, Vertical / Q000517:prevention & control*; D010567:Pertussis Vaccine / Q000008:administration & dosage*; D011247:Pregnancy; D011251:Pregnancy Complications, Infectious / Q000517:prevention & control*; D011295:Prenatal Care / Q000379:methods; D016896:Treatment Outcome; D022282:Vaccines, Acellular / Q000008:administration & dosage; D017778:Vaccines, Combined / Q000008:administration & dosage; D014917:Whooping Cough / Q000453:epidemiology / Q000517:prevention & control*
chemical_list: D010567:Pertussis Vaccine; D022282:Vaccines, Acellular; D017778:Vaccines, Combined