Teens’ Tdap booster dose begins to wane after 2 years

In the study by Acosta et al., the duration of Tdap effectiveness is disappointing, particularly because case-control studies tend to inflate efficacy. The resurgence of pertussis is often attributed to the switch from whole-cell pertussis vaccines to acellular products. However, the increase in reported pertussis began 14 years before the universal use of diphtheria-tetanus-acellular pertussis (DTaP) vaccines in childhood commenced. The two greatest contributors to the resurgence of pertussis are greater awareness and more sensitive diagnosis (routine use of polymerase chain reaction).

In the pre-DTaP and pre-Tdap eras, the pertussis attack rate in nonepidemic periods in largely whole-cell pertussis vaccine–primed adolescents and adults was 370 to 500 per 100,000 per year. These rates are underestimates because of clear evidence of “observer bias” in both studies. In this present Washington State study, the attack rate during the epidemic was only 182.3 per 100,000 for the one-half-year study period.

Factors that I think are most important relating to DTaP vaccine failure are as follows: decay in antibody over time; a T helper (Th) 1/Th2 versus a Th1, Th17 cellular response; incomplete antigen package; incorrect balance of antigens in the vaccine; linked-epitope suppression; and the occurrence of pertactin-deficient B. pertussis strains. Some, but not all, of these factors also may relate to Tdap failure over time.

Although adequate data are not available, it can be assumed that adolescents and adults who were primed in infancy by infection or DTP will have a Th1, Th17 response to Tdap. In contrast, those who were primed by DTaP will have a Th1/Th2 response. In line with the results of these two recent Tdap effectiveness studies, we should examine our present Tdap immunization recommendations. It is my opinion that we should continue with our present Tdap schedules. Of most importance is to see that all pregnant women receive Tdap with each pregnancy. This alone can prevent virtually all pertussis deaths in young infants.

James D. Cherry, M.D., is professor of pediatrics at the University of California, Los Angeles. These comments are excerpted from an editorial (Pediatrics 2015 [doi:10.1542/peds.2014-4118]) accompanying Dr. Acosta’s study. Dr. Cherry is a member of the Sanofi Pasteur speakers bureau and of the Global Pertussis Initiative, supported by Sanofi Pastuer. He receives royalties from Elsevier for “Feigin and Cherry’s Textbook of Pediatric Infectious Diseases.”