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Pertussis vaccine effectiveness fades over time

Tuesday November 27, 2012
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In an examination of cases of childhood pertussis in California, researchers found that children with pertussis had lower odds of having received all five doses of the diphtheria, tetanus and acellular pertussis vaccine series, according to a study.

In addition, the odds of having pertussis increased as the time since last DTaP dose lengthened, which is consistent with a progressive decrease in estimated vaccine effectiveness each year after the final dose of DTaP vaccine, researchers reported in the Nov. 28 issue of the Journal of the American Medical Association.

"Pertussis remains a poorly controlled vaccine-preventable disease in the United States, despite a well-established childhood vaccination program and high coverage," researchers wrote in background information for the study. "No study, to our knowledge, has compared fully vaccinated with unvaccinated children to estimate the durability of protection afforded by the childhood series."

Lara K. Misegades, PhD, MS, of the Centers for Disease Control and Prevention in Atlanta, and colleagues conducted a study to evaluate the association between pertussis and receipt of five DTaP doses by time since the fifth DTaP dose in 15 California counties. They examined 682 suspected, probable and confirmed pertussis cases among children ages 4 to 10 reported from January through Dec. 14, 2010. They compared those cases to 2,016 children in the same age group who received care from the clinicians reporting the cases. Vaccination histories were obtained from medical records and immunization registries.

Cases were more likely than controls to be unvaccinated (7.8% vs. 0.9%), female and older. Compared with controls, children with pertussis had 89% lower odds of having received all five doses of DTaP. When children were categorized by time since completion of the series, using an unvaccinated reference group, children with pertussis were less likely than controls to have received their fifth dose within the prior 12 months, 2.8% versus 17.6%

This association was evident with longer time since vaccination, with odds ratios increasing with time since the fifth dose. At 60 months or longer, the estimated vaccine effectiveness was 72.1%. The estimated relative decline in vaccine effectiveness was 27.4% from less than 12 months to 60 months or longer since the fifth DTaP dose. Accordingly, the estimated vaccine effectiveness declined each year after receipt of the fifth dose of DTaP.

"The increasing incidence of pertussis, changing epidemiology and demonstrated decline in the estimated DTaP vaccine effectiveness over time have raised concern about the current U.S. pertussis vaccine and may prompt consideration of alternative schedules," the authors wrote. "Ultimately, improved control of pertussis may require a vaccine that provides longer duration of protection or differently affects transmission in the community."

In an accompanying editorial, Eugene D. Shapiro, MD, of the Yale University School of Medicine and Yale Graduate School of Arts and Sciences in New Haven, Conn., wrote that the "most important consideration is to try to protect infants, who have the most morbidity and mortality from pertussis. Ö Immunization of all pregnant women and of all household and day-care contacts (both adults and children) of children younger than 1 is one important strategy that may help alleviate this problem.

"Public health authorities will need to assess the feasibility and safety of different schedules for administering currently available vaccines, including the possibility of shorter periods between primary and booster doses (more frequent administration of tetanus toxoid may be associated with more severe local adverse reactions)."

The study is available at http://jama.jamanetwork.com/article.aspx?articleid=1456072.


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