Vaccine-Preventable Diseases

Haemophilus influenzae type b

Haemophilus influenzae type b (Hib) was the most common cause of bacterial meningitis and a leading cause of other serious invasive infections in young children before the introduction of Hib vaccines. About 55% to 65% of affected children had meningitis, the remainder suffering from epiglottitis, bacteremia, cellulitis, pneumonia or septic arthritis. The case-fatality rate of meningitis is about 5%. Severe neurologic sequelae occur in 10% to 15% of survivors and deafness in 15% to 20% (severe in 3% to 7%). H. influenzae is also commonly associated with otitis media, sinusitis, bronchitis and other respiratory tract disorders. However, since type b organisms seldom cause these disorders, Hib vaccines have not affected their incidence.

Universal immunization against Hib has led to a significant reduction in the incidence of invasive Hib disease in Canada. The protection resulting from infant immunization appears to be long lasting, and no cases have been reported to date in fully immunized, healthy adolescents.

Epidemiology

Since the introduction of Hib vaccines in Canada in 1988, the overall incidence of reported disease has decreased from 2.6 per 100,000 (686 cases) in 1988 to 0.3 per 100,000 (81 cases) in 2004. During this period, the number of reported cases among children < 5 years of age has fallen by almost 97%, from 526 to 17 cases. In 2004, the incidence was 2.4 per 100,000 children < 1 year of age and 0.7 per 100,000 children between the ages of 1 and 5 years. The majority of pediatric cases occur in unimmunized children or in children too young to have received their primary series.

Between 2001 and 2003 only 29 Hib cases were reported in children < 16 years of age by the 12 centres involved in the Immunization Monitoring Program, ACTive (IMPACT) enhanced surveillance program across the country. Only two cases occurred in fully vaccinated, previously healthy children. Twenty of the 29 cases had received no or incomplete primary vaccination, of whom 11 were children < 6 months of age. In addition, eight cases were in children with either an immunodeficiency or other chronic illness.

Non-typeable H. influenzae as well as other non-b typeable H. influenzae can rarely cause invasive disease. In Canada, only invasive Hib disease is under national surveillance. Between 2000 and 2004, 51 cases of invasive H. influenzae were detected in northern Canadian regions participating in the International Circumpolar Surveillance (i.e., Yukon, Northwest Territories, Nunavut and northern regions of Quebec and Labrador). Of these, only five cases (11% of 47 with serotype information) were due to serotype b. Fifty-five percent of cases were caused by serotype a, and 28% of invasive disease involved non-typeable isolates. Serotypes c, d and e were isolated in one case each of invasive disease.

The risk of Hib meningitis is at least twice as high for children attending full-time day care as for children cared for at home. The risk is also increased among children with splenic dysfunction (e.g., sickle cell disease, asplenia) or antibody deficiency, and among Inuit children. In 2002, a possible association between receipt of a cochlear implant and development of bacterial meningitis was identified. Persons who have received a cochlear implant should also be considered at high risk of invasive Hib disease.

Source: Canadian Immunization Guide, 7^th edition, 2006

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Links to more information

Guidelines and Recommendations

• For information about Haemophilus vaccine, see the Canadian Immunization Guide, 7^th edition 2006
  

Information Sheets

• Childhood Immunization - It's Your Health