Meningococcal Vaccine
The meningococcus can be divided into groups by special laboratory tests. Most infections are caused by Groups A, B, C, Y, and W135. In Canada between 1995 and 2003, Group B strains caused 42% of cases or an average of 81 cases per year. The frequency of group B cases does not vary very much from year to year. However, the number of cases caused by group C, Y and W135 varies from year to year. While Group C has traditionally been dominant, the disease landscape has changed in recent years with an increasing numbers of Groups Y and W-135 being observed. Over the 9 year period, group B caused 810 cases, group C 775 cases, group Y 267 cases, and group W135 81 cases. Since 2000, there has been an increase in the frequency of cases caused by groups Y and W135, especially in Ontario.
Group A strains causes large epidemics somewhere in Africa almost every year and epidemics have also occurred in India, Pakistan, Nepal, and China in recent years. There have been no group A epidemics in Canada or USA for over 50 years.
Local outbreaks of meningococcal disease in which 2 or more cases occur in a school or college have been occurring in Canada and other countries for the past 10-12 years. Most of these outbreaks have been caused by Group C strains.
As with pneumococcal and Hib vaccines, the meningococcal vaccines most commonly used in Canada today are the conjugated polysaccharide vaccines.
A combined Groups A-C-Y-W135 Conjugate Vaccine (Menactra®) was approved for use in Canada in May 2006 in children 2 years of age and older, adolescents and adults. The polysaccharides have been linked to a protein (diphtheria toxoid). This vaccine provides much broader protection than other meningococcal vaccines. Because there has been an increase in the frequency of disease caused by groups Y and W135 in Canada, USA, and other parts of the world, the broader coverage provided by the combined A-C-Y-W135 conjugate vaccine makes it preferable to the pure polysaccharide vaccine or to the C conjugate vaccine.
The combined A-C-Y-W135 conjugate vaccine is very safe. Local reactions in children and adolescents are similar to those seen with the A-C-Y-W135 polysaccharide vaccine or with diphtheria-tetanus toxoid. Fever and other systemic reactions are mild and brief in duration. The vaccine produces very high antibody concentrations against all four polysaccharides. Protective levels of antibodies persist for at least 4 years. This vaccine is available as part of the routine childhood vaccine in PEI and new Brunswick. It is also routinely used to immunize all recruits in the Canadian Forces. In other provinces/territories, it must be purchased by parents.
Three new Meningococcal Group C Conjugate Vaccines composed of the purified polysaccharide linked to a protein have been approved for use in Canada. The brand names of the conjugate vaccines are:
- Meningitech(tm)
- Menjugate C®
- Neis-Vac C®
The polysaccharide vaccines do not stimulate adequate immune responses in infants. As a result, the vaccine does not protect children under two years of age from Group C disease. The duration of protection after immunization with the polysaccharide vaccines is thought to be 3 to 5 years in adults and less in children.
The polysaccharide vaccines are not recommended for routine use because:
- They are not effective in children less than 2 years of age, the age group with the highest rate of disease;
- Protection does not last more than 3-5 years so that frequent boosters would be necessary.
The A-C-Y-W135 polysaccharide vaccine (Menomune®) is given to all new recruits in the Canadian forces and to travelers to countries were epidemics are occurring. The vaccines has also been used when an outbreak occurs in a school, university, or community to stop additional cases. Over 2.5 million children and adolescents have received this vaccine in Canada.
Three new Meningococcal Group C Conjugate Vaccines composed of the purified polysaccharide linked to a protein have been approved for use in Canada. The brand names of the conjugate vaccines are:
- Meningitech(tm)
- Menjugate C®
- Neis-Vac C®
The group C conjugate vaccines are very safe and stimulate production high levels of protective antibodies in infants and young children. Studies in Canada of infants immunized with the conjugate vaccines at 2, 4, and 6 months of age showed that local tenderness, redness, and swelling occurred less frequently after the group C conjugate vaccine than after the combined diphtheria-tetanus-acellular pertussis-polio vaccine (PENTACEL®). Rates of fever, irritability, crying, and other systemic reactions were not increased by the addition of the group C conjugate vaccine. Over 15 million infants and children have received the conjugate C vaccine: no serious reactions have been observed.
The meningococcal C conjugate vaccine protects only against disease caused by group C strains. It does not protect against disease caused by other groups of meningococci. Starting November 1999, a large scale immunization program was undertaken in England and Wales to immunize all children less than 18 years of age with the group C conjugate vaccine and to use the vaccine for routine immunization of all infants starting at 2 months of age. Use of the vaccine has been very successful in controlling all forms of disease caused by group C meningococcus. Similar programs have been started in other European countries. The meningococcal C conjugate vaccine is now available at no cost to parents throughout Canada.
In Alberta, the C conjugate vaccine is administered at 2, 4, and 6 months of age; in British Columbia at 2 and 12 months of age; and in the rest of Canada, a single dose is given at 1 year of age. In addition, most provinces recommend routine vaccination of children at 10-14 years of age with one dose of group C conjugate vaccine.
Follow-up studies in England have shown that a single dose of the C conjugate vaccine protects against group C disease for 4-5 years in children 2 years and older. However, the duration of protection seems to wane much more rapidly in infants vaccinated between 2 and 23 months of age. It is recommended that a booster dose be given to children vaccinated before their second birthday in order to provide more lasting protection. An additional booster at 10-14 years of age may also be necessary.
The older polysaccharide vaccines are not recommended for routine use because:
- They are not effective in children less than 2 years of age, the age group with the highest rate of disease;
- Menjugate C®
- Protection does not last more than 3-5 years so that frequent boosters would be required to maintain immunity.
The original polysaccharide vaccines are effective in older children and adults. This vaccine is made of purified polysaccharides extracted from bacteria of several different groups of meningococci. Two forms of the vaccine are available in Canada:
- Combined groups A-C-Y-W135 polysaccharides (Menomune®)
- Combined groups A-C polysaccharides (Mencevax AC®)
The A-C-Y-W135 polysaccharide vaccine (Menomune®) is given to all new recruits in the Canadian forces and to travelers to countries were epidemics are occurring. The vaccines has also been used when an outbreak occurs in a school, university, or community to stop additional cases. Over 2.5 million children and adolescents have received this vaccine in Canada.
No vaccine is available yet for group B strains. This is a major gap in protection against meningococcal disease since group B strains cause 30-60% of cases every year and are particularly common in infants less than 2 years of age. Research to develop an effective group B vaccine is underway in several countries, including Canada.
