In the United States, children receive five doses of diphtheria, tetanus, and acellular pertussis (DTaP) vaccine before 7 years of age.
The duration of protection after five doses of DTaP is unknown.
We assessed the risk of pertussis in children in California relative to the time since the fifth dose of DTaP…
[A]fter the fifth dose of DTaP, the odds of acquiring pertussis increased by an average of 42% per year.
Protection against pertussis waned during the 5 years after the fifth dose of DTaP.
[S]ince the 1980s, despite high levels of vaccine coverage in children, outbreaks of B. pertussis have occurred every 3 to 5 years, with an increase in the peak incidence with each successive outbreak.
Receipt of five doses of DTaP is mandatory for school entry in many states, including California, with the fifth dose usually administered in children between 4 and 6 years of age. Nonetheless, in 2010, California had a large pertussis outbreak, with the highest incidence rates since 1958.
Regardless of the initial effectiveness, the protection from disease afforded by the fifth dose of DTaP among fully vaccinated children who had exclusively received DTaP vaccines waned substantially during the 5 years after vaccination.
Disease-free intervals after pertussis vaccination have decreased over the past two decades…
The incidence of pertussis was highest among the population of children who were 8 to 11 years of age and who had received the full five-dose series of DTaP in childhood…
Our study has limitations. First, although we estimated that the fifth dose of DTaP became 42% less effective each year, we could not anchor this estimate to the initial effectiveness of the vaccine because of the absence of an unvaccinated population.
Second, it is possible that PCR testing misclassified a small fraction of persons (i.e., false positive and false negative tests). Since it was highly unlikely that such potential misclassification depended on the time since immunization, misclassification would imply that DTaP effectiveness may have waned even more than we estimated.
In conclusion, our evaluation of data from a large pertussis outbreak in California showed that protection from disease after a fifth dose of DTaP among children who had received only DTaP vaccines was relatively short-lived and waned substantially each year.