AGGLUTININS IN CHILDREN VACCINATED WITH THE DPT VACCINES USED IN FINLAND, SEROTYPES OF BORDETELLA PERTUSSIS STRAINS ISOLATED DURING WHOOPING COUGH EPIDEMICS IN 1976–1977 AND WHOOPING COUGH ATTACK RATE IN CHILDREN IN THE EPIDEMIC AREAS.

The purpose of this study was to find an answer to the question of why whooping cough cases occur in Finland in spite of the high acceptance rate of DPT vaccine. To this end agglutinins 1,2 and 3 were determined in children vaccinated in 1962–1976 with vaccine A, manufactured by the National Public Health Institute, Helsinki. The amount of agglutinins 1 and 2 was unmeasurable, while an agglutinin 3 titre of±40 was obtained in 9/14(64%). This vaccine contains strain no. 18 530, which is serotype 1.2.3. Vaccine B from the same manufacturer contains strains 18 530 and 1 772, both of which are serotype 1.2.3. In children vaccinated with vaccine B since 1976 the agglutinin 1 titre was±20 in 14/18 (78%) cases. A similar titre of agglutinin 2 was obtained in 14/19 (74%) of cases and of agglutinin 3 in 5/19 (26%). A titre of±40 was obtained for agglutinin 1 in 4/18(22%) cases, for agglutinin 2 in 5/19 (26%) cases and for agglutinin 3 in 14/19 (74%) cases. Of the Bordetella pertussis strains isolated during two whooping cough epidemics in 1976–1977, 83 were serotyped. All these strains were serotype 1.2. The whooping cough attack rate was estimated in 242 incompletely and 44 completely vaccinated children during the epidemics in question. Of the incompletely vaccinated children 188/242(78%) contracted whooping cough and 54/242(22%) remained healthy. Of the completely vaccinated children 17/44(38%) contracted whooping cough and 27/44(62%) remained healthy.