Polysaccharide and conjugated meningococcal vaccines
Internationally marketed meningococcal polysaccharide vaccines are bivalent (A and C), trivalent (A, C and W-135) or tetravalent (A, C, Y and W-135). The vaccines are purified, heat-stable, lyophilized capsular polysaccharides from meningococci of the respective serogroups.
Both group A and group C vaccines have documented short-term efficacy levels of 85–100% in older children and adults. However, group C vaccines do not prevent disease in children under 2 years of age, and the efficacy of group A vaccine in children under 1 year of age is unclear. Group Y and W-135 polysaccharides have been shown to be immunogenic only in children over 2 years of age.
A protective antibody response occurs within 10 days of vaccination. In schoolchildren and adults, the bivalent and tetravalent polysaccharide vaccines appear to provide protection for at least 3 years, but in children under 4 years the levels of specific antibodies decline rapidly after 2–3 years.
The currently available bivalent and tetravalent meningococcal vaccines are recommended for immunization of specific risk groups as well as for large-scale immunization, as appropriate, for the control of meningococcal outbreaks caused by vaccine-preventable serogroups (A and C, or A, C, Y, W-135 respectively). Travellers who have access to the tetravalent polysaccharide vaccine (A, C, Y, W-135) should opt for this rather than the bivalent vaccine because of the additional protection against groups Y and W-135.
These vaccines do not provide any protection against other serogroups such as group B and group X meningococci, which are important causes of meningococcal disease in some countries.
Precautions and contraindications – polysaccharide vaccine
The internationally available polysaccharide vaccines are safe, and significant systemic reactions have been extremely rare. The most common adverse reactions are erythema and slight pain at the site of injection for 1–2 days. Fever exceeding 38.5 ºC occurs in up to 2% of vaccinees. No significant change in safety or reactogenicity has been observed when the different group-specific polysaccharides are combined into bivalent or tetravalent meningococcal vaccines.
Type of vaccine:
1) Purified bacterial capsular polysaccharide meningococcal vaccine (bivalent, trivalent or tetravalent)
2) Conjugate vaccines against A, C, Y, and W135
3) Conjugate MenA vaccine
Number of doses: One
Duration of protection: For 1 and 2: 3–5 years or more; for 3: not known
Contraindications: Serious adverse reaction to previous dose
Adverse reactions: Occasional mild local reactions; rarely, fever
Before departure: 2 weeks
Consider for: 1 and 2: all travellers to countries in the sub-Saharan meningitis belt and to areas with current epidemics; Hajj and Umrah pilgrims (required); 3: a cheaper alterative to 1 and 2 for travellers to highly endemic African countries
Special precautions: Children under 2 years of age are not protected by the vaccine
Conjugate meningococcal vaccines
A T-cell-dependent immune response is achieved through conjugation of the polysaccharide to a protein carrier. Conjugate vaccines are therefore associated with an increased immunogenicity among infants and prolonged duration of protection.
Monovalent serogroup C conjugate vaccines were first licensed for use in 1999 and are now incorporated in national vaccination programmes in an increasing number of countries. In contrast to group C polysaccharide vaccines, the group C conjugate vaccine elicits adequate antibody responses and immunological memory even in infants who are vaccinated at 2, 3 and 4 months of age. Cross-protection does not occur and travellers already immunized with conjugate vaccine against serogroup C are not protected against other serogroups.
In 2010, a conjugated serogroup A meningococcal vaccine designed particularly for use in the African “meningitis belt”received regulatory approval in India and in a few African countries. This vaccine, which is licensed for single-dose immunization of individuals 1–29 years of age, has proved to be safe and highly immunogenic. The conjugate MenA vaccine has been used in large vaccine campaigns in Burkina Faso, Mali and Niger and is being progressively introduced in countries of the African meningitis belt.
Two tetravalent conjugate vaccines against serogroups A, C, Y and W-135 have been licensed in North America and are gradually becoming available in several other countries. In the United States and Canada these vaccines are licensed for individuals 2–55 years of age. A two-dose series of one of these vaccines is licensed also for children aged 9–23 months. These vaccines are expected to induce protection of similar efficacy to, but of longer duration than, that induced by the polysaccharide tetravalent meningococcal vaccine.