Effectiveness of a trivalent serogroup A/C/W135 meningococcal polysaccharide vaccine in Burkina Faso, 2003.

Following a large Neisseria meningitidis W135 (NmW135) epidemic in Burkina Faso (BF) during 2002, a newly licensed trivalent A/C/W135 meningococcal polysaccharide vaccine was introduced in 2003. We conducted a case-control study to assess the vaccine effectiveness (VE) against meningococcal disease. Thirty-two N. meningitidis A (NmA) and 3 NmW135 meningitis cases were enrolled and matched by age-neighborhood to 103 controls. After adjusting for confounding risk factors, VE against NmA or NmW135 was 83.6% (95% CI 31.8-97.0, p=0.01) for persons with verified vaccination. VE against probable/definite NmA alone was 94.0% (95% CI 58.7-99.0, p=0.0003). Low number of NmW135 cases did not allow estimation of VE against NmW135 alone. The vaccine was highly effective against the epidemic. Since 2003, the trivalent vaccine continues to be effectively used in Africa for the control of meningococcal disease epidemics.

The first large epidemic of meningococcal disease caused by serogroup W135, Burkina Faso, 2002.

In 2001 a significant proportion of cases of meningococcal meningitis toward the end of a serogroup A epidemic in Niger and Burkina Faso was found to be caused by serogroup W135 meningococci. The World Health Organization put in place in several African countries an extended surveillance scheme in preparation for a possible epidemic situation. In January 2002, the first large epidemic of meningococcal disease caused by serogroup W135 started in Burkina Faso, resulting in more than 12,000 cases and 1400 deaths. We report here the results of the laboratory-based surveillance and the characteristics of the epidemic clone.

Predictors of immunity after a major serogroup W-135 meningococcal disease epidemic, Burkina Faso, 2002.

BACKGROUND: The African meningitis belt undergoes recurrent epidemics caused by Neisseria meningitidis serogroup A. During 2002, Burkina Faso documented the first large serogroup W-135 (NmW-135) meningococcal disease epidemic. To understand the emergence of NmW-135, we investigated meningococcal carriage and immunity. METHODS: Immediately after Burkina Faso's epidemic, we conducted a cross-sectional survey of meningococcal carriage and seroprevalence in an epidemic and a nonepidemic district. We identified predictors of elevated NmW-135 serum bactericidal activity (SBA), a functional correlate of protection, using multivariate logistic regression. RESULTS: The NmW-135 carriage rate was 25.2% in the epidemic district and 3.4% in the nonepidemic district (P<.0001). Compared with residents of the nonepidemic district, those of the epidemic district had higher geometric mean titers of NmW-135 SBA (P<.0001). NmW-135 SBA titers>or=1:8, an estimated protective threshold, were observed in 60.4% and 34.0% of residents of the epidemic and nonepidemic district, respectively (P=.0002). In a multivariate model, current NmW-135 carriage, age, and residence in the epidemic district were independent predictors of having an NmW-135 SBA titer>or=1:8. CONCLUSIONS: Extensive NmW-135 carriage and transmission in the epidemic area caused residents to acquire natural immunity. Serial carriage and seroprevalence surveys could establish the duration of immunity in the population. The persistent circulation of NmW-135 underscores the potential for periodic NmW-135 epidemics in Africa.