Bordetella pertussis serotype of clinical isolates in Sweden during 1970-1995 and influence of vaccine efficacy studies.

During the years 1970 to 1995, the serotypes of collected clinical isolates from the different regions of Sweden were examined. Vaccination using whole-cell pertussis vaccine decreased during the year preceding cessation of general vaccination of children in 1979. Although the total number of clinical isolates examined was limited up to 1978 compared to later years, serotype 1, 2, 3 clinical isolates generally predominated. During periodical pertussis outbreaks, serotype 1, 3 strains were isolated, the proportion of which was about equal to that of serotype 1, 2, 3 isolates. Following cessation of general vaccination in 1979, the proportion of both serotypes 1, 2, 3 and 1, 3 isolates gradually diminished, together contributing about 20 percent of the total number of isolates in 1995. Clinical isolates of serotype 1, 2 were identified in the year 1977, just before cessation of general vaccination in Sweden using whole-cell vaccine. Since then, this serotype has gradually increased to over 80 percent of total isolates in 1995, possibly indicating that the use of whole-cell pertussis vaccine was effective against this serotype or that the vaccine influenced serotype expression. Vaccine efficacy studies conducted in Sweden during 1986-87 using one and two-component vaccines (BIKEN) and in 1994-95 using two-component (SmithKline Beecham Pharmaceuticals) and five-component (Connaught Laboratories, Ltd.) vaccines are examined with the object of studying whether the vaccines showed any influence on the different serotypes of B. pertussis causing disease.