CMAJ • January 4, 2005; 172 (1). doi:10.1503/cmaj.1031861.
© 2005 Canadian Medical Association or its licensors
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Invasive Haemophilus influenzae type b infections in vaccinated and unvaccinated children in Canada, 2001–2003

David Scheifele, Scott Halperin, Barbara Law and Arlene King for The Canadian Paediatric Society / Health Canada Immunization Monitoring Program, Active (IMPACT)

From the British Columbia's Children's Hospital, Vancouver, BC (Scheifele); IWK Health Centre, Halifax, NS (Halperin); Winnipeg Children's Hospital, Winnipeg, Man. (Law); and Health Canada, Ottawa, Ont. (King)
Immunization Monitoring Program, Active (IMPACT) investigators and participating centres: Dr. Scott Halperin, IWK Health Centre, Halifax, NS; Dr. Robert Morris, Dr. Charles A. Janeway Child Health Centre, St. John's, Nfld.; Dr. Pierre Déry, Centre hospitalier universitaire de Québec (Pavilion CHUL), Quebec, Que.; Dr. Marc Lebel, Hôpital Sainte-Justine, Montréal, Que.; Dr. Dorothy Moore, Montreal Children's Hospital, McGill University Health Centre, Montréal, Que.; Dr. Nicole Le Saux, Children's Hospital of Eastern Ontario, Ottawa, Ont.; Dr. Elizabeth Ford-Jones, The Hospital for Sick Children, Toronto, Ont.; Dr. Barbara Law, Winnipeg Children's Hospital, Winnipeg, Man.; Dr. Ben Tan, Royal University Hospital, Saskatoon, Sask.; Dr. Taj Jadavji, Alberta Children's Hospital, Calgary, Alta.; Dr. Wendy Vaudry, Stollery Children's Hospital, Edmonton, Alta.; Dr. David Scheifele, British Columbia's Children's Hospital, Vancouver, BC; Drs. Arlene King and Wikke Walop, Health Canada liaisons, Ottawa, Ont.; Dr. Joanne Embree, Canadian Paediatric Society liaison, Winnipeg, Man.; Dr. John Waters, Alberta Health liaison, Edmonton, Alta. (deceased)

Background: Although vaccination of infants against Haemophilus influenzae type b (Hib) invasive infections is effective and has been routinely available in Canada since 1992, cases of the disease continue to occur. We were interested in determining whether recent cases of Hib infection reflected progressive loss of protection with time since vaccination, increasing nonacceptance of vaccination or a deleterious effect of coadministration of recently introduced vaccines such as those for pneumococcal and meningococcal conjugates and hepatitis B. We report on the causes of Hib infections among vaccinated and unvaccinated children between 2001 and 2003 in Canada.

Methods: Through our established network of 12 pediatric tertiary care hospitals we actively searched for cases in each centre by reviewing daily admissions and laboratory reports, visiting the wards and checking discharge diagnosis codes. Culture-confirmed cases were summarized by nurse monitors using a standardized reporting system.

Results: We identified 29 cases during the 3 years: 16 in 2001, 10 in 2002 and 3 in 2003. Half of the 29 patients had meningitis. Hib infection was more common among children less than 6 months of age (11 cases) and in boys (20 cases). Two deaths occurred (7% case-fatality ratio). A total of 20 children had received no or incomplete primary vaccination because of parental refusal (7 cases), because they were too young to have completed the primary series (11 cases, including 1 in which parental refusal was also a factor) or because of delays in completing the primary series (2 cases); the vaccination history was uncertain in the remaining case. Infection despite primary vaccination occurred in 9 children: 2 previously healthy children and 7 who were immunocompromised or who had a predisposing condition. None of the cases identified in 2003 involved children who had received any of the newly introduced vaccines.

Interpretation: Invasive Hib infections remain rare in Canada, with most cases occurring in children too young to have completed the primary series. Protection after vaccination appears to extend into later childhood and does not appear to be diminished by coadministration of newer infant vaccines.




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