Invasive Haemophilus influenzae type b infections in vaccinated and unvaccinated children in Canada, 2001-2003.
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.


CONCLUSIONS
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.
Scheifele
David
D
British Columbia's Children's Hospital, 4500 Oak St., Vancouver BC V6H 3N1. dscheifele@cw.bc.ca
Halperin
Scott
S
Law
Barbara
B
King
Arlene
A
Halperin
Scott
S
Morris
Robert
R
Janeway
Charles A
CA
Déry
Pierre
P
Lebel
Marc
M
Moore
Dorothy
D
Le Saux
Nicole
N
Ford-Jones
Elizabeth
E
Tan
Ben
B
Jadavji
Taj
T
Vaudry
Wendy
W
Walop
Wikke
W
Embree
Joanne
J
Waters
John
J
D002170:Canada / Q000453:epidemiology; D002648:Child; D002675:Child, Preschool; D006192:Haemophilus Infections / Q000453:epidemiology* / Q000517:prevention & control / Q000821:virology; D018073:Haemophilus Vaccines; D019741:Haemophilus influenzae type b; D006776:Hospitals, Pediatric; D006801:Humans; D007223:Infant; D008297:Male; D008583:Meningitis, Haemophilus / Q000453:epidemiology / Q000517:prevention & control; D011159:Population Surveillance
D018073:Haemophilus Vaccines