Reemergence of pertussis in the highly vaccinated population of the Netherlands: Observations on surveillance data

We analyzed pertussis reporting, death, hospitalization, and serodiagnostic data from 1976 to 1998 to help explain the cause of the 1996 pertussis out break in the Netherlands. The unexpected outbreak was detected by an increa se in pertussis reporting and by other surveillance methods. In 1996, accor ding to reporting and serologic data, the increase in pertussis incidence a mong (mostly unvaccinated) children less than 1 year of age was similar to the increase in hospital admissions. Among older (mostly vaccinated) person s, the increase in hospital admissions was relatively small. The increase i n pertussis incidence was higher among vaccinated than among unvaccinated p ersons of all ages. This resulted in lower estimates of vaccine effectivene ss. The proportion of pertussis infections resulting in recognizable sympto ms may have increased among vaccinated persons because of a mismatch of the vaccine strain and circulating Bordetella pertussis strains. The small imm unogenicity profile of the Dutch vaccine may have resulted in greater vulne rability to antigenic changes in B. pertussis.