Results with a new DTP vaccine in Japan.

Adverse reactions to DTP became a social problem in Japan in 1975 which brought a fall of immunization rates and an epidemic of pertussis which had its peak in 1979. Development of a new DTP vaccine with less adverse reactions was urgently needed and an acellular pertussis vaccine was developed which has replaced whole cell pertussis vaccines. More than 15 million doses of the new DTP vaccine has been administered since 1981 in Japan. Immunization acceptance reached 80% in 1982 and the incidence of pertussis has shown a definite decline. Temperature elevation to 38 degrees C or above following immunization with the new DTP vaccine occurred in approximately 1% of all vaccinees. Local reactions were less frequent after the first dose but observed in 40-50% of vaccinees after the second or later doses. However, local reactions were transient and subsided within a few days. Three cases who developed CNS symptoms have been reported for an incidence of 0.19 per one million doses. Attack rates in home contacts below 5 years of age were 84.2% in non-vaccinees and 5.5% in children who had received two or more doses of DTP. The estimated efficacy rate was 93.5%. Anti-LPF and anti-FHA titers after two or three doses of DTP were similar to those in the convalescent stage of natural pertussis infections. Antibody titers of children immunized with the new DTP were similar to those of children immunized with whole cell pertussis vaccines.