Limitations of current vaccines

Meningococcal polysaccharide vaccines against serogroups A, C, W135, and Y have been available for more than 20 years and are highly effective in preventing disease in adults and older children. They are also effective in controlling epidemics in Africa. However, these vaccines have several shortcomings that preclude their incorporation into routine immunization programs or the Expanded Program on Immunization (EPI):

• They have limited efficacy in young children, the group most at risk of disease,
• They do not provide long-lasting protection,
• They do not confer herd immunity, that is, they do not decrease transmission of the organism in the population.

In addition,

• Polysaccharide vaccines may not protect against all forms of carriage (how the disease is transmitted from one person to the next). In this particular case, they may not protect against nasopharyngeal carriage
• Repeated doses of capsular polysaccharide (CPS) vaccines have been associated with hyporesponsiveness.

For these reasons, polysaccharide vaccines have been primarily used for control of outbreaks or epidemics, or for use in travelers to areas of the world where disease is present.

In Africa, repeated vaccination of the broad target age group is programmatically very difficult. A conjugate vaccine that provides longer-term protection at all ages and that confers herd immunity would be far better suited for prevention of meningococcal epidemics in the region.

Photo Credit: Benoît Lange (left); Benoît Lange (right)

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