Epidemiological determinants of pertussis

In countries with pertussis immunisation programmes, the main epidemiological determinant of the disease is the quality of protection induced by the vaccine and the coverage level achieved. Epidemiological data from England and Wales provide strong evidence that whole-cell pertussis vaccines can give good protection against both clinical disease and transmission of infection, and can generate herd immunity at high coverage levels. Models of pertussis transmission indicate that, even in the absence of waning immunity, the incidence of the disease is likely to increase in older age groups in countries with sustained high coverage. Active surveillance to detect the occurrence of pertussis in adults is required as the ascertainment of such cases through passive clinical reporting systems is low. Comprehensive post-licensing surveillance of the effectiveness of acellular pertussis vaccines will be essential to assess their long-term protection against both clinical disease and transmission of infection, and to determine the optimum boosting strategy.