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Acellular pertussis vaccine provided limited protection
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.
Perspective
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During the past few weeks, there have been numerous newspaper reports and television and radio segments about pertussis and pertussis vaccine failures. Most recently, the focal point of the programs and reports were a perspective piece that I wrote (N Engl J Med. 2012;367:785-787) and a paper on waning protection following the fifth dose of DTaP by Klein and colleagues (Engl J Med. 2012;367:1012-1019). The latter paper presented data on 277 children in Northern California with pertussis. However, a more complete data set with more straight forward information involving 9,154 pertussis cases in California in 2010 was published in June 2012 (Winter K. Pediatrics; published online July 23, 2012). Both of these studies show an increased number of DTaP vaccine failures over time following the fifth dose of DTaP.
Although these data are clearly alarming we should look at this in the context of the big picture and formulate both short- and long-term plans to cope with the problem. This has already been done for the short-term by both the ACIP and the Committee on Infectious Diseases of the American Academy of Pediatrics. Morbidity and mortality due to pertussis is greatest in young infants so that cocoon strategies need to be employed. The most practical strategy for this is immunization of pregnant women in the second or third trimester. Also, vigorous attempts should be made to immunization others who will have contact with young infants (fathers, grandparents and older children and adolescents in the household). In addition we need to find ways to immunize all adults with Tdap and plan for a booster schedule like that already recommended for Td.
Data from the 1990s clearly showed that DTaP vaccines were less efficacious than DTP vaccines. Both of our present vaccines have primary efficacies in children of about 70%. For the long-term, but starting immediately, the CDC, NIH and Center for Biologics Evaluation and Research of the FDA, along with selected pertussis experts, should work on developing new and better vaccines.
Finally, it should be recognized that even in the present pertussis epidemic years, there are approximately 20-fold fewer pertussis cases reported today than occurred in the prevaccine era.