Fractional Dose Tetravalent A, C, Y, W135 Meningococcal Polysaccharide Vaccine

• To measure the immunogenicity of a dose corresponding to one fifth of the amount of the licensed meningococcal A/C/Y/W135 polysaccharide vaccine, i.e. 10µg for each component
  
• To measure the immunogenicity of a dose corresponding to one tenth of the licensed meningococcal A/C/Y/W135 polysaccharide vaccine, i.e. 5µg for each component
  

• To determine the pharyngeal carriage of N. meningitidis and in particular W135 strains in the study population
  
• To determine the natural immunity towards N. meningitidis serogroup A, C, Y and W135 before immunisation in the study population
  
• To measure a possible waning of immunity at one year and at two years after immunisation
  
• To measure the immune response after challenging with a second dose of the commercialised meningococcal A/C/Y/W135 polysaccharide vaccine after one year, in a group of volunteers who have received a reduced dose on day 0
  

In 2002, an epidemic of meningococcal disease started in Burkina Faso and Neisseria meningitidis serogroup W135 was identified as the causative organism. This event followed the outbreaks of 2000 and 2001 in Mecca, Saudi Arabia, and was the first large epidemic caused by serogroup W135. Mass vaccination of the population with the only vaccine protecting against W135, i.e. the tetravalent A/C/Y/W135 polysaccharide vaccine (TPSV), was not possible because of the global shortage in supply, in addition to its cost. In 2003, GlaxoSmithKline (GSK) produced a trivalent polysaccharide vaccine A/C/W135 for US$ 1.5. This vaccine was used in Burkina Faso in the new epidemic faced by this country in 2003. However, availability and affordability of the tetravalent A/C/Y/W135 polysaccharide vaccine and of the trivalent A/C/W135 polysaccharide vaccine are still under discussion between the WHO and the producers. The risk of further epidemics due to the W135 strain in other African countries is of high concern for the scientific community.

The current dose of the licensed tetravalent A/C/Y/W135 polysaccharide vaccine contains 50 μg of each polysaccharide component. During the 1980’s, researchers from the Walter Reed Army Institute of Research (WRAIR) did extensive works on the immunogenicity of meningococcal polysaccharide vaccines in adults. A first study performed by Griffiss et al. demonstrated that doses of 5 μg of group Y and group W135 polysaccharides were as effective as doses of 50 μg in inducing production of bactericidal antibody amounts correlating with functional immunity (Griffiss et al. Mil Med 1985; 150: 529-33). A second study concluded that doses of 7.5 μg (Y and W) and 15 μg (A and C) were sufficient to induce equivalent binding and bactericidal antibody responses as 50 μg (Griffiss et al. Infect Immun 1982; 37: 205-8). In a more recent study from Granoff et al., 1/50 (1 mcg) of the ordinary dose of tetravalent A/C/Y/W135 vaccine was given (Granoff et al. J Infect Dis 1998; 178: 870-4). The antibody responses to A and C have been measured, and this low dose was sufficient to mount a C response in most of the subjects, but the dose was less effective in eliciting a response to A. The antibody responses to W135 and Y were not reported.

Hypothesis:

Lower doses of each A/C/Y/W135 component of the meningococcal polysaccharide vaccine could confer a similar functional immunogenic response as the dose of 50 μg currently being used, and subsequently be equally protective.

It would potentially bring two major benefits. Firstly, it would increase the number of tetravalent vaccine doses available on the market. Secondly, it would decrease the cost of the individual vaccine dose. As a result, more people could be vaccinated, and thereby protected against the disease, and to a lower price.

Results obtained with the study on the tetravalent A/C/Y/W135 polysaccharide vaccine would be valid for the trivalent A/C/W135 polysaccharide vaccine.