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Waning of pertussis immunity in older children prompted recommendations for a booster dose of acellular pertussis vaccine in pre-adolescence. Declining immunity during the first 2 years of life has not been examined as closely. In a matched case-control study from Australia, investigators examined the efficacy of the primary series of diphtheria-tetanus-acellular pertussis (DTaP) vaccine in children younger than 5 years during a countrywide outbreak of pertussis (2008–2011). The 18-month DTaP booster was eliminated in 2003, leaving three primary doses at ages 2, 4, and 6 months with subsequent doses at age 4 years and during adolescence.
Among 4584 confirmed cases of pertussis (age range, 2–47 months) and healthy controls matched for age, re…