Overview of Vaccines
There are several safe and very effective vaccines to protect against major causes of bacterial meningitis. The vaccines work by stimulating the immune system to create protective antibodies against the bacteria. Antibodies are proteins which bind to the bacteria and help destroy them. If protective antibodies are present in the blood at the time the bacteria try to invade into the bloodstream from the nose and throat, the antibodies and white blood cells rapidly kill the bacteria and prevent illness from developing. The antibodies also protect by preventing infection of the nose and throat by the bacteria. This protection reduces the spread of the meningitis bacteria between people.
There are many different strains of bacteria that cause meningitis. It is necessary to protect yourself against each one because the antibodies resulting from each vaccine are specific. A vaccine for one bacterium or strain will not protect against other strains.
There are four types of vaccines:
- pure polysaccharide;
- polysaccharide linked or conjugated to a protein;
- purified outer membranes of the bacteria without any inner contents;
- proteins derived from the outer lining of the bacteria.
The first two types contain the purified polysaccharide (a complex sugar) which forms the outer coat or capsule of the bacteria. The pure polysaccharide vaccines are not effective in infants less than 2 years of age. The conjugated polysaccharide vaccines, on the other hand, are effective at all ages, starting in infants as young as 2 months of age.
Conjugated vaccines are composed of the purified polysaccharides chemically linked to a protein such as diphtheria toxoid or tetanus toxoid. Conjugated vaccines are known to offer a longer duration of immunity than polysaccharide vaccines. Such vaccines also stimulate immune memory cells so that the immune system responds more rapidly and with a greater production of antibodies when a booster dose is given.
Conjugated vaccines against the meningococcus, pneumococcus, and Haemophilus influenzae type b, the three major causes of bacterial meningitis, are now part of the routine childhood immunization program in Canada and many other countries.
Vaccines prepared from the outer membrane of the bacteria consist of the empty membrane shell. Such vaccines have been used to control outbreaks of group B meningococcal disease. They are effective against the outbreak strain, but not against the many other group B strains.
Finally, 2 vaccines composed of several purified proteins derived from the outer membrane of group B meningococcus has been developed for use in infants, children, and adolescents. These proteins are made by isolating the gene responsible for their production and recombining the gene with the DNA of E. coli, the common intestinal bacteria. The E. coli, as it grows in the laboratory, makes the proteins from the meningococcus. These proteins are then isolated and purified to make the MenB vaccine. It has been approved for use against group B meningococcous in Canada, USA, the European Union, England, Ireland and Australia. The MenB vaccines are available in Canada for purchase, but have not been added to any provincial/territorial immunization programs.
Vaccines Against Meningococcus
Below is a list of the vaccines for the different forms of meningitis.
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. Two new vaccines against group B have been approved for use in Canada in 2013.
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 vary very much from year to year. However, the number of cases caused by group C, Y and W do vary from year to year. The frequency of Group C disease has decreased significantly since the introduction of routine immunization with Group C conjugate vaccine in 2005-6 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 per year between 2007-2011.. The average annual number of cases caused by serogroup W and Y since 2007 were 11 and 34 respectively.
Children across Canada are routinely vaccinated with one of the conjugated group C vaccines (Menjugate C® or NeissVac C®) that protect only against disease caused by group C at 1 year of age or earlier. In addition, many provinces also use these vaccines in children in school-based programs between 10-13 years of age.
Conjugated ACYW vaccine protects against meningococcal disease caused by groups A,C,Y and W-135. It can be used in children 2 years of age and older previously vaccinated against Group C, thereby serving as a booster of immunity to group C while also providing protection against groups A, Y, and W. It can also be used in children 2 years of age and older who have not previously been vaccinated with any meningococcal vaccine.
In Alberta, New Brunswick, Newfoundland and Labrador, Ontario, Prince Edward Island, and Saskatchewan and in new recruits in the Canadian Forces, Conjugated ACYW vaccine has replaced the group C conjugate vaccine for routine use in adolescents in the provincial immunization program. It is hoped that other provinces will do the same to maximize protection against meningococcal disease.
Studies have shown that the conjugated ACYW vaccine is also effective in infants, but a series of injections is required to induce immunity, as with other infant vaccines. It is likely that the 4-in-1 will replace the group C conjugated vaccine currently used in infants.
Unfortunately the polysaccharide of group B meningococci is not effective as a vaccine. Two new vaccines against group B strains has been developed which contains purified proteins from the bacteria which are very important in enabling the bacteria to cause disease. The vaccines have been shown to be safe and very effective in stimulating the immune system to make antibodies which kill most strains of group B. Both vaccines are safe and effective in infants, children and adults. The vaccines have been approved for use in Canada, the USA, European Union, England, Ireland, New Zealand and Australia. The vaccines are not included in any of the routine immunization programs in Canada and must be purchased for use.
There are over 80 types of this bacterium. They are primary causes of pneumonia, bronchitis, ear and sinus infections. Less frequently they cause meningitis.
The conjugated pneumococcal vaccine used in Canada today contains 13 different polysaccharides which protect against the 13 most common types causing disease in children less than 5 years of age. The original pneumococcal vaccine contained 7 polysaccharides and was very effective in preventing disease caused by those 7 types. However, it has no effective on other strains, some of which increased in frequency as disease from the original 7 decreased. The new vaccine contains the original 7 plus 6 additional strains needed to cover most of the disease-causing types. New vaccines containing up to 25 different types of pneumococci are being developed.
Haemophilus influenza type b
Hib was the most common cause of bacterial meningitis until 1992. It also caused other serious infections including pneumonia, severe throat infections, skin and joint infections. Infants from 6 to 18 months and children under the age of 5 were most commonly infected. Hib infections are rare in Canada because since 1992 infants have been routinely immunized with Hib vaccine. In Canada, the conjugated Hib vaccine is given to infants at 2, 4, 6, and 18 months of age as part of a combined 5-in-1 vaccine containing diphtheria toxoid, tetanus toxoid, acellular pertussis vaccine, and inactivated polio vaccine.