The 10 paediatric centres that participated in the Immunization Monitoring Program, ACTive (IMPACT) in 1995 determined that in 1985, before the first Haemophilus influenzae type b vaccine became available, they admitted 485 cases for treatment in hospital. In 2000, with 12 centres participating, the case total was four. This historic low number represents more than a 99% reduction in cases compared with the preimmunization era. Two of the cases in 2000 occurred despite age-appropriate immunization. This is a remarkably small number of vaccine failures, indicating a high level of effectiveness of the current conjugate vaccine. This was the first year that none of the cases of Haemophilus influenzae type b occurred in children whose parents had declined to immunize them. In other recent years, about 25% of cases resulted from failure to immunize children appropriately.
Footnotes
IMPACT is a program of the Canadian Paediatric Society and Health Canada’s Centre for Infectious Disease Prevention and Control that monitors vaccine-associated adverse events, vaccine failures and selected infections in children that are, or are soon to be, preventable by vaccines