Pediatrics
March 2014, VOLUME 133 / ISSUE 3
http://pediatrics.aappublications.org/current.shtml

Article
Duration of Protection After First Dose of Acellular Pertussis Vaccine in Infants
Helen E. Quinn, PhD, MAEa,b, Thomas L. Snelling, BMBS (Hons), Grad Dip Clin Epidc,
Kristine K. Macartney, MBBS, BMedSci, MDa,b, and Peter B. McIntyre, MBBS, PhDa,b
Author Affiliations
aNational Centre for Immunisation Research and Surveillance of Vaccine Preventable Diseases, and
bDiscipline of Paediatrics and Child Health, University of Sydney, The Children’s Hospital at Westmead, Westmead, New South Wales, Australia; and
cTelethon Institute for Child Health Research, Centre for Child Health Research, The University of Western Australia, West Perth, Western Australia, Australia
http://pediatrics.aappublications.org/content/133/3/e513.abstract

Abstract
OBJECTIVE: Data on the effectiveness of the diphtheria–tetanus–acellular pertussis (DTaP) vaccine in the first 4 years of life are sparse. We evaluated the vaccine effectiveness (VE) of 1 and 2 doses of DTaP before 6 months of age and of 3 doses from 6 months of age in Australia, where, since 2003, a fourth dose is not given until 4 years.

METHODS: We matched reported pertussis cases aged 2 to 47 months between January 2005 and December 2009 to controls from a population-based immunization register by date of birth and region of residence. VE by number of doses and age group was calculated as (1 – odds ratio) × 100%.

RESULTS: VE against hospitalization increased from 55.3% (95% confidence interval [CI], 42.7%–65.1%) for 1 dose before 4 months of age to 83.0% (95% CI, 70.2%–90.3%) for 2 doses before 6 months. The VE of 3 doses of DTaP against all reported pertussis was 83.5% (95% CI, 79.1%–87.8%) between 6 and 11 months, declining to 70.7% (95% CI, 64.5%–75.8%) between 2 and 3 years of age and 59.2% (95% CI, 51.0%–66.0%) between 3 and 4 years of age.

CONCLUSIONS: DTaP provided good protection against pertussis in the first year of life from the first dose. Without a booster dose, the effectiveness of 3 doses waned more rapidly from 2 to 4 years of age than previously documented for children >6 years of age who had received 5 doses.