Hospital-based active surveillance of childhood pertussis in Austria from 1996 to 2003: estimates of incidence and vaccine effectiveness of whole-cell and acellular vaccine.

BACKGROUND: This study was undertaken to analyse the epidemiology of pertussis disease among hospitalised children during the transition period from whole-cell to acellular pertussis vaccine in order to compare the respective estimates of vaccine effectiveness.
METHODS: Surveillance was conducted between 1 January 1996 and 31 December 2003. The data originated from a voluntary hospital-based surveillance network including all 44 nationwide paediatric departments.
RESULTS: The mean annual hospitalisation incidence for children decreased over time, from 27.9 per 100,000 population in 1996 to 6.8 cases per 100,000 population in 2003. The mean age of reported hospitalised pertussis cases was 4.7 years (+/- 5.5 S.D.), increasing from 4.06 years (+/- 4.6 S.D.) in 1996 to 5.5 years (+/- 8.6 S.D.) in 2003. Estimated vaccine effectiveness (after three vaccine doses) was 79% for the whole-cell versus 92% for the acellular pertussis vaccine. A significantly higher proportion (19%) of fully immunised children among hospitalised patients was observed for the years where only acellular pertussis vaccine was used compared to whole-cell vaccine era (2%) which was, however, mainly due to children above 2 years of age.
CONCLUSIONS: Our results imply that despite high vaccination coverage rate, pertussis is still a considerable cause of hospital admissions in children in Austria where it remains to be shown that the novel vaccination strategy of additional booster doses in adolescents and adults will control disease in the long term.