What if a Child has Never been Immunized?

Children in Canada are routinely immunized against nine infectious diseases: diphtheria, tetanus, pertussis, poliomyelitis, Haemophilus influenzae type b (Hib) infection, measles, mumps, rubella and hepatitis B. Vaccines for these diseases are administered following immunization schedules that vary slightly between provinces and territories (1). A varicella vaccine was licensed in Canada in December 1998 (2), but is not yet routinely used in most provincial or territorial childhood programs (Prince Edward Island is initiating a childhood varicella immunization program in 2000). Despite high overall vaccine coverage (estimated at 82% to 95% for individual vaccine antigens when assessed at 24 months of age [3]), there remain individuals or pockets of children in Canada who are susceptible to infection because they have never been or are incompletely immunized against one or more of these nine infectious diseases. New immigrants from countries who have not had one or more of the above-mentioned childhood vaccines make up part of this never-immunized group, especially if ‘catch-up’ immunizations are not provided after their arrival in Canada (4). Some children are not immunized because they have valid medical contraindications (5), they missed immunization appointments or their parents declined to have the children immunized. Some parents have religious reasons for declining the immunizations, while others hold mistaken beliefs that the infectious diseases either do not cause serious harm or no longer occur in Canada (6). Infectious diseases that are rare in Canada, such as diphtheria and poliomyelitis, may be reintroduced into the country from abroad. Cases of measles, mumps, rubella, pertussis, tetanus, Hib and hepatitis B are still reported in Canada. Examples include the recent outbreaks of rubella in Manitoba (7) and mumps in British Columbia (8). Because the immunization coverage in Canadian children is generally high, physicians may wrongly assume that children are fully immunized by the time that they enter school. Children’s immunization records should be checked to ensure that the children’s immunization are up-to-date whenever they are exposed to vaccine-preventable infections. Table 1 (middle column) outlines the preventive steps that physicians and public health authorities recommend when faced with a susceptible child who has been exposed to one of these infections. This often involves one or a combination of the following steps: using immune globulin preparations to provide immediate protection; starting the primary immunization series to provide either immediate (eg, postexposure immunization for measles, varicella and hepatitis A) or future protection; prescribing antibiotic prophylaxis; and excluding the child from school or daycare to prevent further exposure or spread of the infection. For fully immunized children, these steps may be eliminated (see Table 1, right-hand column for comparison). Parents should be encouraged to inform their physicians when their unimmunized child is exposed to a vaccinepreventable illness so that the appropriate steps can be taken during a bona fide exposure. Unbeknownst to the parents, a susceptible child may be exposed to infectious persons who are asymptomatic or the child may sustain a wound that becomes contaminated with Clostridium tetani and tetanus may develop without an opportunity to provide preventive measures. Parents of unimmunized children are often unaware that a blood product (immune globulin) may be administered in the absence of prior immunity to certain infections. A ‘catchup’ primary immunization series that is initiated only after exposure has occurred will not usually induce immunity in time to prevent or reduce the severity of the infection (with the exception of measles, varicella and hepatitis A, where postexposure immunization is effective in preventing illness). Therefore, avoiding the primary series during infancy simply delays the immunization until after an infectious exposure has occurred. Adults who were not immunized during childhood may travel abroad and be exposed to these vaccine-preventable infectious diseases in foreign countries. In developing countries, health care may not be readily available, thereby increasing the risk of morbidity or mortality from these infectious diseases. Furthermore, colleges offering medical, veterinary, dental, nursing and laboratory technology degrees require students to

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