Pertussis Vaccine Efficacy Varies by Age, Wanes Over Time

Jennifer Garcia

April 28, 2014

A new study has found that the current pertussis vaccine (diphtheria-tetanus-acellular pertussis [DTaP]) decreased the risk of developing the disease across all age cohorts; however, immunity appeared to wane in children between 7 and 10 years of age. In addition, the results, published online April 18 in Clinical Infectious Diseases, suggest that the Tdap booster provides less protection, even in recently immunized adolescents.

Despite the inconsistent protection, Juventila Liko, MD, MPH, from the Oregon Immunization Program, Portland, and colleagues emphasize the value of pertussis vaccination. "Our data demonstrate the effectiveness of pertussis vaccination among all age cohorts of children: no matter the age, an unvaccinated child was more likely to contract pertussis than a vaccinated or partially vaccinated child," they write.

The authors identified 709 pertussis cases in 2012 among children aged 2 months to 19 years of age, according to data from the Oregon reportable disease database. Vaccination records were obtained from the Oregon Immunization Information System.

Of the confirmed pertussis cases, 45% (129/289) of those between 2 months and 6 years of age were up to date with the diphtheria-tetanus-acellular pertussis vaccine schedule, as were 79% (129/153) of those between 7 and 10 years of age.

Among adolescents 13 to 16 years of age or older, 76% of cases had received the Tdap booster.

On the basis of these data, the researchers estimate vaccine effectiveness "ranged from 95% (95% CI [confidence interval], 92%–97%) among children 15–47 months of age to 47% (19%–65%) among adolescents 13–16 years of age."

The authors found that "being unvaccinated against pertussis was significantly associated with higher disease incidence for every age cohort studied, with relative risks ranging from 1.9 to 20.6." In addition, there was a 1.3- to 3.0-fold risk of developing pertussis among children who were only partially vaccinated.

"Even when we see epidemic disease, we find that the vaccine is protective," noted Dr. Liko in an interview with Medscape Medical News.

When asked whether they would recommend any changes to public policy on the basis of this data, Dr. Liko said no, but that, "public health officials should continue to reassure that vaccination as recommended by [the Advisory Committee on Immunization Practices] is associated with lower risk of pertussis among children and adolescents."

The authors acknowledge limitations of the study, such as not attempting to measure the potential waning of immunity between early childhood and adolescence, as well as a possible effect of incomplete reporting to state databases on incidence rates.

The study authors suggest the possibility of waning immunity, given the increase in risk for pertussis seen among children aged 7 to 10 years, despite their high rate of vaccination; however, Dr. Liko pointed out that the duration of efficacy of the pertussis vaccine remains unknown and will require further evaluation. The authors also note that changes in vaccine effectiveness among children aged 13 to 16 years may also be secondary to the transition between 1997 and 1999 from a whole-cell to an acellular vaccine formulation.

In conclusion, Dr. Liko said, "Physicians should be reassured that one is better off with vaccination than without and that declining the vaccine carries a significant risk for contracting pertussis."

Funding for this study was provided by the Emerging Infections Program Cooperative from the Centers for Disease Control and Prevention. The authors have disclosed no relevant financial relationships.

Clin Infect Dis. Published online April 18, 2014. Abstract

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