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In 2010, California had a large pertussis outbreak among children, many of whom were fully vaccinated. Investigators examined the duration of protection after a fifth dose of the diphtheria, tetanus, and acellular pertussis vaccine (DTaP; given between ages 47 and 84 months) in a case-control study of Kaiser Permanente Northern California members who had polymerase-chain-reaction (PCR) pertussis tests between 2006 and 2011. The researchers compared 277 children (age range, 4–12 years) who were PCR positive for pertussis, 3318 PCR-negative children, and 6068 matched controls.
Older children had a higher percentage of pertussis cases than younger children (range, 4.5% in 6-year-olds to18.5% in 10-year-olds). Children with pertussis had a significantly longer time since the fifth DTaP dose and received that dose earlier than controls. The risk for pertussis increased 42% each year after the fifth dose of DTaP.
Klein NP et al. Waning protection after fifth dose of acellular pertussis vaccine in children. N Engl J Med 2012 Sep 13; 367:1012. (http://dx.doi.org/10.1056/NEJMoa1200850)
Comment
Some of the increase in reported cases of pertussis might reflect more awareness and better PCR testing. However, the increase also coincides with the shift from whole-cell to acellular pertussis vaccines. The incidence of pertussis during the 2010 outbreak decreased sharply among teens older than 12 years, many of whom had received the whole-cell vaccine and presumably had longer lasting immunity. Although no recommendations have been made to change the current vaccine schedule, this resurgence indicates that longer-lasting vaccines or earlier boosters should be investigated.