Strains of Meningococcus
There are several strains of meningococcus. The most common are called Groups A, B, C, Y and W. Vaccines are used routinely to protect against groups ACYW. A new vaccine against group B was approved for use in Canada in 2013. A second vaccine against group B was approved for use in Canada in 2018.
In Canada since 2007, Group B strains have caused almost 60% of cases or an average of 111 cases per year. The frequency of group B cases does not change very much from year to year. However, the number of cases caused by group C, Y and W do vary over time. The frequency of Group C disease has decreased significantly since the introduction of routine immunization with Group C conjugate vaccine in 2002 - 1-6 in infants and older children. From a peak of 202 cases in 2001, the number of group C cases decreased by 90%, to an average of 19 cases between 2007-2011. The average annual number of cases caused by serogroup W and Y since 2007 were 11 and 34 respectively.
Group A strains causes large epidemics 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 65 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 since 1989. Although Group C strains caused most of these outbreaks prior to 2005, group C outbreaks have become rare in the USA and Canada because of vaccines. Today, most outbreaks of invasive meningococcal disease in North America are now caused by group B strains. The new group B vaccines have been effective in controlling such outbreaks.
As with pneumococcal and Hib vaccines, the meningococcal vaccines most commonly used in Canada today are the conjugated polysaccharide vaccines.
Three meningococcal group C Conjugate Vaccines composed of the purified polysaccharide linked to a protein carrier have been approved for use in Canada. The brand names of the conjugate vaccines are:
Menjugate CÂ® and NeisVac-C.
The group C conjugate vaccines are very safe and stimulate production high levels of protective antibodies in infants, children and adolescents. Studies in Canadian infants immunized with the conjugate vaccines at 2, 4, and 6 months of age showed that local tenderness, redness, and swelling occur. Rates of fever, irritability, crying, and other systemic reactions were not increased by the addition of the group C conjugate vaccine. Many millions infants and children have received the conjugate C vaccine: no serious reactions have been observed.
The National Advisory Committee on Immunization recommends at least one dose of group C vaccine at 12 months of age of age. Vaccination prior to this can be done, but he 12 month dose is always needed.
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.
Three conjugate vaccines that protect against Groups ACYW have been approved for use in Canada in children 2 years of age and older, adolescents and adults and one for children 2 months of age and older. The polysaccharides have been linked to a protein (diphtheria toxoid, Menactra®; CRM protein, Menveo®, or tetanus toxoid, Nimenrix). These vaccines provide much broader protection than group C conjugated vaccine. Increase in the frequency of disease caused by groups Y and W have been observed in Canada, the USA, England, and other parts of the world. Therefore, the broader coverage provided by the combined ACYW conjugate vaccine makes it preferable to the C conjugate vaccine.
The combined ACYW conjugate vaccines are very safe. Local reactions in children and adolescents are similar to those seen with other vaccines. Fever and other systemic reactions are mild and brief in duration.
The vaccines produce very high antibody concentrations against ACWY meningococci. Protective levels of antibodies persist for at least 4 years. This vaccine is used in school-based programs across Canada as well as for new recruits joining the Canadian Forces.
Recent studies have demonstrated that the combined ACYW conjugated vaccines are safe and effective in stimulating immunity in infants. However, several injections are required in the infant series, as with other infant vaccines.
A new vaccine [Bexsero®] against serogroup B meningococci was approved for use in Canada in 2013 and in other countries. The vaccine has been studied in infants, children, and adolescents and is approved for use from 2 months to 25 years of age the list is long where this has been approved.
A second vaccine against Group B strains [TRUMENBA™] was approved for use in Canada in 2018 in children and young adults 10-25 years of age.
Neither group B vaccine has been introduced into routine vaccine programs in Canada, but are available for purchase by parents and for outbreak control. Bexsero was used to control an epidemic in Quebec in 2014. Children 2 months to 20 years of age were immunized.
The new B vaccine consists of purified proteins derived from the outer surface of group B meningococci, combined with the outer membrane vaccine used in New Zealand during the outbreak of group B disease. The use of multiple components in the vaccine is necessary in order to provide protection against the many different group B strains.
The B vaccines have been shown to be effective in inducing antibodies which kill at least 80% of group B strains. Such antibodies are protective against disease.
The B vaccines are also safe. No serious adverse events have been reported after its use. Local reactions at the site of the injection occur in about 20% of children. The redness, swelling, and pain are usually mild and last only a day or so. Severe reactions are very rare. Bexsero is associated with an increased rate of fever in infants at 2, 4, and 6 months of age, when it is given at the same visit as the routine infant vaccines. The fever is usually between 39-40°C and rarely lasts more than 48 hours. The National Advisory Committee on Immunization recommends using Acetominophen routinely when administering this vaccine.
One of the new Group B vaccines (Bexsero®) has been introduced into the routine infant vaccine schedule in England and has proven to be effective in preventing group B disease. Both new group B vaccines require a 2 dose primary schedule and will require boosters to maintain protection against group B disease.