Polysaccharide vaccines for preventing serogroup A meningococcal meningitis

Randomised trials carried out over two decades ago showed that the polysaccharide vaccine prevented serogroup A meningococcal meningitis. Subsequent non-randomised studies, however, suggested significant variations in the age-specific duration of protection among young children.

The aim of the review was to determine the effect of polysaccharide serogroup A vaccine for preventing serogroup A meningococcal meningitis. The specific objectives were to assess the age-specific effects of the vaccine, the effect of booster doses in children under five years of age, and the duration of protection in children and adults.

In 2004, the review was updated. The following databases were searched for records of new trials: the Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library Issue 4, 2004); MEDLINE (January 1966 to November Week 1 2004); and EMBASE (January 1990 to September 2004).

The first stage of the review included randomised trials. The second stage included non- randomised studies that addressed specific outcomes not answered by the randomised trials.

One reviewer assessed the methodological quality of the randomised trials and two reviewers independently identified and assessed the non-randomised studies. Of the twelve eligible Randomized trials, four were excluded because of the high risk of bias in assessing vaccine efficacy. Data from the trials were pooled using the Exact method to assess vaccine efficacy at one, two and three years post vaccination. Of the 15 non-randomised studies, only two addressed the specific objectives not answered by the randomised trials but were assessed to be at high risk of bias.

The protective effect within the first year of vaccination was consistent across the randomised trials, and the summary vaccine efficacy was 95% (95% confidence interval (CI) 87% to 99%). Protection extended into the second and third year after vaccination but the results did not attain statistical significance. The vaccine was protective in Finnish children aged 3 months to five years. The latter was also the only trial that assessed the effect of a booster dose in children under two years of age but lacked power to yield statistically significant results. The vaccine was protective in one- to five-year old children in developing countries (Nigeria and Sudan) but the age-specific efficacy in strata between one and five years of age could not be determined.

For the first year after vaccination, the polysaccharide serogroup A vaccine was strongly protective against serogroup A meningococcal meningitis in participants over five years of age. It was also protective beyond the first year after vaccination in this age group but the level of vaccine efficacy could not be determined with precision. Children aged one to five years in developing countries were also protected but the level of efficacy in this age group could not be determined. While the vaccine was strongly protective among children aged three months to five years in developed countries the level of efficacy across age strata within this age group could not be determined. The number of children aged under two years was too small to draw conclusions on the protective effect of a booster dose of vaccine.