Current epidemiology of pertussis in Japan

Since the introduction of whole cell pertussis vaccine into general use as part of the routine immunization in 1947 under the Preventive Immunization Law, a steady decrease in reported cases of pertussis was noted until 1974. At that time the number of reported cases reached an all time low and no deaths caused by pertussis were reported. The vaccine (diphtheria-tetanus-whole cell pertussis vaccine) had been given to infants 12 weeks old or older in a 0.5-ml dose by deep subcutaneous injection; three doses were given at intervals of 3 to 8 weeks and the fourth dose (booster) was given 12 to 18 months after the third dose. The immunization was completed with those four doses. Because whole cell vaccine appeared to be associated with severe neurologic illnesses, it was temporarily suspended in 1975. The vaccine was resumed soon thereafter but the age of administration was raised to 24 to 48 months. Under these circumstances acceptance rates of pertussis occurred, reaching a peak in 1979. Although whole cell vaccine was used even after temporary suspension, it was considered to be unacceptable by the public. As a result the acellular pertussis vaccine was developed and has totally replaced whole cell vaccine since 1981. A steady decrease in reported cases of pertussis as well as the number of deaths has been noted since 1979 in accordance with increase in vaccine acceptance rates. The national surveillance system begun in 1981 demonstrated also a steady decrease in the incidence of pertussis during the past 9 years.