Waning protection following 5 doses of a 3-component diphtheria, tetanus, and acellular pertussis vaccine

Background: The effectiveness of diphtheria, tetanus, and acellular pertussis (DTaP) vaccines wanes substantially after the 5^th dose given at ages 4-6years, but has not been described following 5 doses of the same type of DTaP vaccine. We investigated waning effectiveness against pertussis in California over nearly 10years, which included large pertussis outbreaks, following 5 doses of GSK DTaP vaccines (DTaP₃).

Methods: We conducted a case-control study (NCT02447978) of children who received 5 doses of DTaP at Kaiser Permanente Northern California from 01/2006 through 03/2015. We compared time since the 5^th dose in confirmed pertussis polymerase chain reaction (PCR)-positive cases with pertussis PCR-negative controls. We used logistic regression adjusted for calendar time, age, sex, race, and service area to estimate the effect of time since the 5^th DTaP dose on the odds of pertussis. Our primary analysis evaluated waning after 5 doses of DTaP₃. We also examined waning after 5 doses of any type of DTaP vaccines.

Results: Our primary analysis compared 340 pertussis cases diagnosed at ages 4-12years with 3841 controls. The any DTaP analysis compared 462 pertussis cases with 5649 controls. The majority of all DTaP doses in the study population were DTaP₃ (86.8%). Children who were more remote from their 5^th dose were less protected than were children whose 5^th dose was more recent; the adjusted odds of pertussis increased by 1.27 per year (95% CI 1.10, 1.46) after 5 doses of DTaP₃ and by 1.30 per year (95% CI 1.15, 1.46) after any 5 DTaP vaccines doses.

Conclusions: Waning protection after DTaP₃ was similar to that following 5 doses of any type of DTaP vaccines. This finding is not unexpected as most of the DTaP vaccines administered were DTaP_3. Following 5 doses of DTaP₃ vaccines, protection from pertussis waned 27% per year on average. NCT number: NCT02447978.