Two primary doses of diphtheria-tetanus-acellular pertussis vaccine induce immunological responses to Bordetella pertussis as strong as those induced by three primary doses.

Pertussis vaccinations are administered worldwide under various conditions and schedules with diphtheria-tetanus-pertussis (DTP). In Japan, a general vaccination with three primary doses of diphtheria-tetanus-acellular pertussis (DTaP) at 4-week intervals and one booster dose 12 months after the primary series have been used since 1981. Decreasing the number of doses of the vaccination would lessen the physical and economic costs. To compare the immunological response to two versus three primary doses, we assessed antibody and cellular immune responses in health children. The anti-filamentous hemagglutinin (anti-FHA) and anti-pertussis toxin (anti-PT) antibody responses to two primary doses of DTaP before a booster were significantly lower than the responses to three primary doses. Although these antibody levels were low in children who received two primary doses, the FHA-induced DNA synthesis was equal to that of the children who received three doses. The anti-FHA and anti-PT antibody levels 4 weeks after the booster following two doses were similar to the levels following three doses, and high antibody titers were maintained over a long period. In areas where contact with bacteria is expected, two primary doses of DTaP may be adequate to induce the necessary level of immunological responses.