[Pertussis in Poland in 1999]

Following marked increase in number of reported cases of pertussis in 1997/1998, the incidence decreased 1999, but still remained higher than in the years 1993-1996. A general trend toward increase of the fraction of older cases is continued since 1992. The cause of this changing pattern may be decreasing level of antibodies against pertussis following immunizations and lack of a buster dose at the age of 5-7 years. Introduction of such an additional dose of vaccine may increase immunity of those older children who at the present time are susceptible.