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.
Following one dose, 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, one dose of these polysaccharide vaccines appears to provide protection for at least 3 years, but in children under 4 years of age the levels of specific antibodies decline rapidly after 2–3 years.
Adverse events and precautions - polysaccharide vaccine
The internationally available polysaccharide vaccines are safe, and significant systemic reactions are very 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 group-specific monovalent vaccines are combined into bivalent or tetravalent meningococcal vaccines.
Special precautions: Children under 2 years of age are not protected
by the vaccine
Conjugate meningococcal vaccines
Conjugation of the bacterial polysaccharide to a protein carrier induces a T-cell-dependent immune response characterizedby increased immunogenicity among infants, prolonged duration of protection, and reduced nasopharyngeal carriage of meningococci. Conjugate meningococcal vaccines are available as monovalent serogroup A and serogroup C vaccines; bivalent serogroups A, C vaccine; and tetravalent serogroups A, C, Y, W-135 vaccine.
These vaccines are highly immunogenic (>90%), although protective antibody titres are not long-lasting in young children. Cross29 protection between different meningococcal serogroups does not occur.
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.
A combination vaccine based on Haemophilus influenza type b and Neisseria meningitidis serogroup C vaccines (HibMecC) is also marketed.
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.
Three tetravalent conjugate vaccines against serogroups A, C, Y and W-135 meningococci are now licensed internationally. They differ in the conjugate carrier protein (CRM 197, tetanus toxoid, and diphtheria toxoid), but all are administered intramuscularly and show similar immunogenicity. In Canada and the United States, these vaccines are licensed for single-dose immunization of individuals 2– 55 years of age. In addition, two of these vaccines offer a two-dose schedule for children aged 9-23 months.
In 2012, a conjugate tetravalent vaccine that can be administered as a single dose from the age of 1 year was licensed in Europe.
Adverse events and precautions– conjugated vaccines
All meningococcal conjugate vaccines have an excellent safety record. None has been associated with any serious adverse effects during clinical trials or in post-marketing surveillance. Redness, swelling and pain at the site of injection may occur, however. Such reactions usually start within the first day after immunization and last 13 days. Less commonly, children may develop a fever or be irritable for a short period.
Travellers should be aware that protection induced by meningococcal vaccines is strictly serotype-specific and that tetravalent vaccine offers the widest range of protection. However, tetravalent meningococcal vaccines do not protect against meningococci of serogroups B and X which are common causes of meningococcal disease in some countries.
Required vaccinations: Saudi Arabia demands proof of recent meningococcal vaccination (tetravalent vaccine) as a visa requirement for pilgrims and guest workers. See 6.4 “Required vaccinations”.