There are currently two vaccines approved for use in preventing meningococcal meningitis which is caused by the bacteria Neisseria meningitidis. The vaccines are the meningococcal conjugate vaccine (MCV4) and the meningococcal polysaccharide vaccine (MPSV4). The MCV4 is recommended for adolescents ages 11 to 18 and some high-risk children between the ages of two and ten, according to the Centers for Disease Control and Prevention. The MPSV4 is recommended for adults.
Microorganism
Both the MCV4 and MPSV4 vaccines contain polysaccharide antigens that are prepared using the outer coating of the bacteria Neisseria meningitidis, which consists of polysaccharides (molecules made up of long sugar chains). Once injected into the body these antigens trigger the formation of antibodies against the bacteria. The MCV4 and MPSV4 vaccines contain extracts from the four most common types of Neisseria meningitidis bacteria: Group A, Group C, Group Y and Group W135.
The difference between the two vaccines comes with the concentration and the delivery of the polysaccharide antigens. The MCV4 vaccine contains four micrograms of each group, while the MPSV4 vaccine contains 50 micrograms of each.
Adjuvant
Adjuvants are ingredients that are added to a vaccine to boost the body's immune response. Vaccines that utilize adjuvants are able to produce a stronger immune response using less of a microorganism. The polysaccharides of the MCV4 vaccine are coupled to 48 micrograms of diphtheria toxoid, which is considered an adjuvant.
Without the diphtheria toxoid, such as is the case with the MPSV4 vaccine, the antigens can only induce an immune response utilizing B-cells which can produce antibodies, but not for a long-term response. In addition, infants do not have mature B-cells and therefore cannot produce antibodies to the MPSV4 vaccine, which is why it is only effective in adults.
The diphtheria toxoid used in the MCV4 vaccine carries the meningococcal antigen components to the cells and is able to induce a T-cell response, which according to the CDC Prevention and Control of Meningococcal Disease is a memory response. The use of the adjuvant also allows for the lower concentration of each polysaccharide used.
Preservative
Preservatives may be added to a vaccine to keep them free of contamination by bacteria or fungi. The most commonly used preservative, thimerosal, is controversial as it contains mercury. The MPSV4 vaccine used to be produced in a 50-dose vial that included 25 micrograms of thimerosal, however that dose vial has been discontinued according to the CDC Prevention and Control of Meningococcal Disease. The single-dose vials of both the MCV4 and MPSV4 do not contain any preservatives.
Excipient
Excipients are inactive substances that are added to vaccines to either aid in the manufacturing of the vaccine or to make the vaccine stable so that the components do not separate. Excipients may also help make the vaccine safe to inject by making the solution the correct pH.
The MCV4 vaccine contains a sodium chloride (table salt) solution that is buffered with sodium phosphate, which is used to keep the pH of the vaccine constant. The MPSV4 vaccine contains lactose, a milk sugar, which helps make the vaccine stable during storage.
