The Diversity of Meningococcal Carriage Across the African Meningitis Belt and the Impact of Vaccination With a Group A Meningococcal Conjugate Vaccine

Abstract

Background: Study of meningococcal carriage is essential to understanding the epidemiology of Neisseria meningitidis infection.

Methods: Twenty cross-sectional carriage surveys were conducted in 7 countries in the African meningitis belt; 5 surveys were conducted after introduction of a new serogroup A meningococcal conjugate vaccine (MenAfriVac). Pharyngeal swab specimens were collected, and Neisseria species were identified by microbiological and molecular techniques.

Results: A total of 1687 of 48 490 participants (3.4%; 95% confidence interval [CI], 3.2%-3.6%) carried meningococci. Carriage was more frequent in individuals aged 5-14 years, relative to those aged 15-29 years (adjusted odds ratio [OR], 1.41; 95% CI, 1.25-1.60); in males, relative to females (adjusted OR, 1.17; 95% CI, 1.10-1.24); in individuals in rural areas, relative to those in urban areas (adjusted OR, 1.44; 95% CI, 1.28-1.63); and in the dry season, relative to the rainy season (adjusted OR, 1.54; 95% CI, 1.37-1.75). Forty-eight percent of isolates had genes encoding disease-associated polysaccharide capsules; genogroup W predominated, and genogroup A was rare. Strain diversity was lower in countries in the center of the meningitis belt than in Senegal or Ethiopia. The prevalence of genogroup A fell from 0.7% to 0.02% in Chad following mass vaccination with MenAfriVac.

Conclusions: The prevalence of meningococcal carriage in the African meningitis belt is lower than in industrialized countries and is very diverse and dynamic, even in the absence of vaccination.

Keywords: Africa; Neisseria meningitidis; carriage; meningitis; meningococcus.

Figure 1.

Carriage prevalence, by country and survey. Asterisks denote postvaccination surveys.

Figure 2.

Carriage prevalence, by age and survey.

Figure 3.

Carriage prevalence, by age and sex (all surveys combined).

Figure 4.

Distribution of Neisseria meningitidis genogroups, by country and survey. The overall prevalence of carriage in each country during the survey is shown in brackets. A, First cross-sectional survey in 2010 (rainy season). At this time, no country had introduced serogroup A meningococcal conjugate vaccine (MenAfriVac). B, Second cross-sectional survey in 2011 (rainy season). At this time, MenAfriVac had been introduced in Mali and Niger, as indicated by asterisks. C, Third cross-sectional survey in 2012 (dry season). At this time, MenAfriVac had been introduced in Mali, Niger, and Chad, as indicated by asterisks.

Figure 5.

Distribution of strain types across the meningitis belt. The number of meningococci isolated in each country is indicated. A, Survey 1 (2010). At this time, no country had introduced serogroup A meningococcal conjugate vaccine (MenAfriVac). B, Survey 2 (2011). At this time, MenAfriVac had been introduced in Mali and Niger, as indicated by asterisks. C, Survey 3 (2012). At this time, MenAfriVac had been introduced in Mali, Niger, and Chad, as indicated by asterisks.