Polysaccharide vaccines for preventing serogroup A meningococcal meningitis.

BACKGROUND

Controlled trials over two decades ago showed that the polysaccharide vaccine prevented meningococcal meningitis. Subsequent observational studies suggested variations in the level and duration of protection, particularly among young children.

OBJECTIVES

To determine the effect of polysaccharide serogroup A vaccine for preventing serogroup A meningococcal meningitis.

SEARCH STRATEGY

MEDLINE and the Cochrane Controlled Trials Register.

SELECTION CRITERIA

Randomised and other prospective controlled trials.

DATA COLLECTION AND ANALYSIS

One reviewer collected data and assessed the methodologic quality of the trials. Data were pooled using the Exact method to assess vaccine efficacy at one, two and three years post-vaccination.

MAIN RESULTS

The protective effect within the first year was consistent across all eight trials, including one with participants exclusively under six years of age (in Finland); overall vaccine efficacy was 95% (Exact 95% CI 87%, 99%). The Finnish trial lacked statistical power to assess the effect of a booster dose given to children less than 18 months old. In the three other trials that included children less than six years old (one in Sudan and two in Nigeria), none of the vaccinated children developed meningitis, but the statistical significance of this finding was undetermined. Protection extended into the second (in two studies) and third (in one study) years after vaccination, but these results were also not statistically significant.

REVIEWER'S CONCLUSIONS: When compared with current recommendations, the methodological quality and relative incompleteness of the published reports could arguably render the trials invalid for this review. However, it was unlikely that the results of the trials in such diverse settings would have been biased towards a strong and consistent protective effect. Immunogenicity trials were not included in this review. Stage two of the review will assess the vaccine effect from observational studies.