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Acellular pertussis vaccine provided limited protection
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A fifth dose of diphtheria-tetanus-acellular pertussis vaccine among children who received only DTaP vaccines was relatively short-lived and waned substantially each year, according to findings of a study conducted during the California pertussis outbreak that began in 2010.
“Our findings highlight the need to develop new pertussis-containing vaccines that will provide long-lasting immunity,” Nicola P. Klein, MD, PhD, and colleagues wrote in a study released today in The New England Journal of Medicine.
The researchers assessed the risk for pertussis in children relative to the time since the fifth dose of DTaP from 2006 to 2011 in California — this included a large outbreak in 2010.
The control study included Kaiser Permanente Northern California members who received DTaP vaccine at 47 to 84 months of age. Children with pertussis confirmed by a positive polymerase chain reaction assay were compared with two sets of controls: children who were PCR negative for pertussis and closely matched controls from the general population of health plan members.
Children who received whole-cell pertussis vaccine during infancy or who received any pertussis-containing vaccine after their fifth dose of DTaP were excluded.
Nicola and colleagues then compared 277 children, aged 4 to 12 years, with positive PCR results for pertussis with 3,318 PCR-negative controls and 6,086 matched controls.
Children with positive PCR results were more likely to have received the fifth DTaP dose earlier than children with negative PCR.
A comparison with PCR-negative controls indicated that the odds of acquiring pertussis increased by an average of 42% per year after the fifth dose of DTaP.
The researchers highlighted two study limitations. First, although it was estimated that the fifth dose of DTaP became 42% less effective each year, during the study the researchers could not anchor this estimate to the initial effectiveness of the vaccine because of the absence of an unvaccinated population. Second, PCR testing may have possibly been misclassified in a small fraction of patients.
Disclosure: The study was funded by Kaiser Permanente. Klein reports receiving grant support to her institution from Sanofi Pasteur, GlaxoSmithKline, Novartis, Merck, and Pfizer.
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