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NACI publishes detailed recommendations pertaining to the use of meningococcal vaccines. Readers are referred to these recommendations for more detailed information(33,46). Recommendations are also contained within the most recent edition of the Canadian Immunization Guide(47). Recommendations are updated as new information becomes available.
Briefly, there are two different types of meningococcal vaccine currently available in Canada: purified capsular polysaccharide vaccines and protein-polysaccharide conjugate vaccines. Polysaccharide vaccines include bivalent vaccine against serogroups A and C (MenAC-Ps) and quadrivalent vaccine for serogroups A,C, Y and W135 (MenACYW-Ps). Three monovalent meningococcal C conjugate vaccines (MenC-conjugate) are currently available: MenjugateTM (Chiron Corporation), Neis Vac-CTM (ID Biomedical Corporation) and MeningitecTM (Wyeth Pharmaceuticals).
Meningococcal C conjugate vaccines are safe, immunogenic and effective, and can be given to children < 2 years of age. The conjugate vaccine is also expected to confer longer duration of immunity compared with the polysaccharide vaccine. In addition to outbreak control, the Public Health Agency of Canada and NACI recommend routine childhood immunization with meningococcal C conjugate vaccine(33,47).
Polysaccharide vaccines cover three additional serogroups compared with conjugate meningococcal C vaccines (i.e. serogroups A, Y, W135), but they are not immunogenic for children < 2 years of age and have a shorter duration of protection. Polysaccharide vaccines are recommended for outbreak control, for the protection of persons travelling to locations with epidemic disease attributable to vaccine serogroups and for persons who may be at increased risk of meningococcal disease. Polysaccharide vaccines are not recommended for routine childhood immunization(33).
Bivalent (A, C) or quadrivalent (A, C, Y, W135) polysaccharide vaccine should be considered for eligible susceptible close contacts of cases with IMD known to be caused by serogroup A; quadrivalent polysaccharide vaccine should be considered for eligible susceptible close contacts of cases of serogroup Y or W135 disease (see section 11.3 for information on revaccination). For susceptible close contacts of known serogroup C disease, meningococcal C conjugate vaccine is preferred because of longer duration of protection and induction of immunologic memory. However, polysaccharide vaccines will provide protection in older children and adults during the 1-year period of increased risk. Polysaccharide vaccines are ineffective against serogroup C disease in children < 2 years of age, and meningococcal C conjugate vaccine should be given to children in that age group. No vaccine is currently available in Canada for contacts of individuals with serogroup B disease.
Vaccination is not generally indicated for contacts of cases of disease in which the serogroup has not been determined. With the increasing use of PCR techniques the sensitivity of diagnosis will improve; sero- group identification should be obtained before immunoprophylaxis where possible. Factors that may assist in decisions regarding whether “empiric” immunization of contacts should be provided include the availability of diagnostic tests, the epidemiologic situation (e.g. there is an outbreak of serogroup Y in the community and the index case is in the at-risk group), and the age and clinical presentation of the case. If a contact has received meningococcal vaccine in the past, decisions regarding revaccination should follow current NACI guidelines (see section 11.3).
Outbreaks of serogroup C meningococcal disease in teenagers and adults may be controlled by use of meningococcal C conjugate or polysaccharide vaccines; however, the use of conjugate vaccine may be preferable because of the induction of immunologic memory and prolonged duration of protection(33). In adults and children previously immunized with a polysaccharide vaccine, antibody response has been found to be lower after a second than after the first dose when the time interval between the two doses is less than the recommended 5 years. This response has been termed “immunologic hypo- responsiveness”(48-50) and has not been observed with conjugate vaccine(48). Adults who have been vaccinated with a second dose of polysaccharide vaccine after the recommended interval have demonstrated an adequate response. The clinical significance of immunologic hyporesponsiveness is unknown, but if revaccination is considered in persons who received polysaccharide vaccine in the past, the use of meningococcal C conjugate vaccine is recommended. In younger children (< 10 years of age) meningococcal C conjugate vaccine is preferred for control of outbreaks in view of superior immunogenicity and efficacy in this age group. Children < 2 years of age should not receive the polysaccharide vaccine for prophylaxis but should complete a full course of conjugate vaccine appropriate to their age, according to the NACI recommended schedule(33).
Outbreaks of meningococcal A disease have not occurred in Canada since the 1940s. If this rare event occurs, polysaccharide vaccine is recommended. Readers are referred to the most recent NACI meningococcal vaccine recommendations for further information(33,46,47). For the control of outbreaks associated with serogroup Y or W135 meningococci, one dose of a quadrivalent polysaccharide vaccine is recommended for persons >= 2 years of age.
The need for and effectiveness of revaccination with polysaccharide vaccine has not been fully established. For persons fully immunized with meningococcal C conjugate vaccine, revaccination is not thought to be necessary at this time, although there are insufficient data to predict persistence of immunologic memory (and presumed protection) beyond 5 years. This recommendation may be revised in the future; further research is warranted. Readers are referred to the most recent NACI meningococcal vaccine recommendations for further information(33,46,47).