Loosening the grip of meningococcal disease in Africa
Authors: Johannes Elias
Journal: The Lancet (2013)

Although incidence rates of meningococcal disease in developed countries have steadily decreased over the past century, the disease remains a formidable public health threat in Africa. The geographical area most affected has been named the meningitis belt and includes countries of the Sahel and sub-Sahel. New findings from the study by Doumagoum Daugla and colleagues1Daugla DM Gami JP Gamougam K et al.Effect of a serogroup A meningococcal conjugate vaccine (PsA–TT) on serogroup A meningococcal meningitis and carriage in Chad: a community trial.Lancet. 2013; (published online Sept 12.)http://dx.doi.org/10.1016/S0140-6736(13)61612-8PubMed Google Scholar in The Lancet confirm the effectiveness of one shot of a glycoconjugate vaccine (serogroup A meningococcal polysaccharide–tetanus toxoid conjugate vaccine [PsA–TT, MenAfriVac]), developed under the Meningitis Vaccine Project (MVP),2LaForce FM Konde K Viviani S Préziosi M-P The Meningitis Vaccine Project.Vaccine. 2007; 25: 97-100Crossref PubMed Scopus (134) Google Scholar against disease caused by and carriage of serogroup A meningococci in Chad. These findings might finally usher in the beginning of elimination of serogroup A meningococci in the meningitis belt, an endeavour that seems theoretically possible in view of the huge success of conjugate vaccines in abolishing disease caused by serogroup C meningococci in England and other countries.3Trotter CL Ramsay ME Vaccination against meningococcal disease in Europe: review and recommendations for the use of conjugate vaccines.FEMS Microbiol Rev. 2007; 31: 101-107Crossref PubMed Scopus (134) Google Scholar Despite the availability and use of polysaccharide vaccines for the control of outbreaks since the 1970s, epidemics caused by serogroup A have continued to recur in the meningitis belt with incidence rates during outbreaks surpassing 300 cases per 100 000 population.4Campagne G Schuchat A Djibo S Ousséini A Cissé L Chippaux JP Epidemiology of bacterial meningitis in Niamey, Niger, 1981–96.Bull World Health Organ. 1999; 77: 499-508PubMed Google Scholar Daugla and coworkers1Daugla DM Gami JP Gamougam K et al.Effect of a serogroup A meningococcal conjugate vaccine (PsA–TT) on serogroup A meningococcal meningitis and carriage in Chad: a community trial.Lancet. 2013; (published online Sept 12.)http://dx.doi.org/10.1016/S0140-6736(13)61612-8PubMed Google Scholar document the successful reduction of disease incidence by 94% after vaccination with PsA–TT, as compared with disease incidence in a region in which the vaccination campaign had not been carried out. Carriage prevalence of the epidemic strain was reduced by 98% after vaccination with PsA–TT. The vaccine's effect on carriage probably explains the absence of cases in residents too old (older than 30 years) or too young (younger than 1 year) to be immunised in vaccinated regions. The complete levelling of the expected rise in incidence in the first quarter of 2012 impressively underscores the potential of PsA–TT for areas affected by serogroup A disease. Results from studies in Burkina Faso, the first country to start vaccination in December 2010, have already shown reduction of disease incidence,5Novak RT Kambou JL Diomandé FV et al.Serogroup A meningococcal conjugate vaccination in Burkina Faso: analysis of national surveillance data.Lancet Infect Dis. 2012; 12: 757-764Summary Full Text Full Text PDF PubMed Scopus (123) Google Scholar elimination of carriage,6Kristiansen PA Diomandé F Ba AK et al.Impact of the serogroup A meningococcal conjugate vaccine, MenAfriVac, on carriage and herd immunity.Clin Infect Dis. 2013; 56: 354-363Crossref PubMed Scopus (174) Google Scholar and a herd effect5Novak RT Kambou JL Diomandé FV et al.Serogroup A meningococcal conjugate vaccination in Burkina Faso: analysis of national surveillance data.Lancet Infect Dis. 2012; 12: 757-764Summary Full Text Full Text PDF PubMed Scopus (123) Google Scholar, 6Kristiansen PA Diomandé F Ba AK et al.Impact of the serogroup A meningococcal conjugate vaccine, MenAfriVac, on carriage and herd immunity.Clin Infect Dis. 2013; 56: 354-363Crossref PubMed Scopus (174) Google Scholar after vaccination with PsA–TT. However, by contrast with Chad, the campaign in Burkina Faso targeted the whole population aged 1–29 years, resulting in the vaccination of more than 11 million people within 10 days.5Novak RT Kambou JL Diomandé FV et al.Serogroup A meningococcal conjugate vaccination in Burkina Faso: analysis of national surveillance data.Lancet Infect Dis. 2012; 12: 757-764Summary Full Text Full Text PDF PubMed Scopus (123) Google Scholar Nevertheless, as incidence rates were already falling sharply since 2007,5Novak RT Kambou JL Diomandé FV et al.Serogroup A meningococcal conjugate vaccination in Burkina Faso: analysis of national surveillance data.Lancet Infect Dis. 2012; 12: 757-764Summary Full Text Full Text PDF PubMed Scopus (123) Google Scholar the reported vaccine effect might have been enhanced by natural waning of the disease. By contrast, the situation in Chad was different; here, regions vaccinated in December, 2011 included only part of the population (roughly 1·8 million people), while extension of enhanced surveillance to a non-vaccinated district (Moissala) allowed concurrent comparison of incidence between vaccinated and unvaccinated areas. The investigators do not detail whether the populations in vaccinated and unvaccinated areas were indeed comparable; additionally, they state that selection of respective areas was not random. However, because disease progression had been consistent in both areas before vaccination, the assumption that the populations were indeed similar is plausible. The presented study design1Daugla DM Gami JP Gamougam K et al.Effect of a serogroup A meningococcal conjugate vaccine (PsA–TT) on serogroup A meningococcal meningitis and carriage in Chad: a community trial.Lancet. 2013; (published online Sept 12.)http://dx.doi.org/10.1016/S0140-6736(13)61612-8PubMed Google Scholar allows a more accurate assessment of vaccine effect than do designs with purely temporal controls.6Kristiansen PA Diomandé F Ba AK et al.Impact of the serogroup A meningococcal conjugate vaccine, MenAfriVac, on carriage and herd immunity.Clin Infect Dis. 2013; 56: 354-363Crossref PubMed Scopus (174) Google Scholar, 7Maiden MCJ Ibarz-Pavón AB Urwin R et al.Impact of meningococcal serogroup C conjugate vaccines on carriage and herd immunity.J Infect Dis. 2008; 197: 737-743Crossref PubMed Scopus (377) Google Scholar Daugla and colleagues' study would not have been possible without the MVP, which exemplifies how an infectious disease can be tackled without the help of multinational companies with little interest in entering markets offering low profit margins. Although the MVP represents an innovative development programme between high-income and low-income countries, it also encourages collaboration between low-income countries—eg, between India as a producer and African countries as consumers of a biotechnology product. This new approach, worthy of replication and extension, was also honoured in the Brazil–Cuba meningitis project.8Thorsteinsdóttir H Sáenz TW Tackling meningitis in Africa.Science. 2012; 338: 1546-1547Crossref PubMed Scopus (4) Google Scholar The report further highlights the urgent need for high quality surveillance systems for the assessment of vaccine effectiveness. However, establishment of high quality surveillance is very challenging, as shown by the inability of researchers, who report implementation of enhanced surveillance in the vaccinated and unvaccinated areas for the duration of the dry season, to estimate one of their system's most basic properties: completeness of case ascertainment.1Daugla DM Gami JP Gamougam K et al.Effect of a serogroup A meningococcal conjugate vaccine (PsA–TT) on serogroup A meningococcal meningitis and carriage in Chad: a community trial.Lancet. 2013; (published online Sept 12.)http://dx.doi.org/10.1016/S0140-6736(13)61612-8PubMed Google Scholar Apart from measurement of vaccine effect, surveillance systems should be able to warn about possible serogroup replacement.9Greenwood B Priorities for research on meningococcal disease and the impact of serogroup A vaccination in the African meningitis belt.Vaccine. 2013; 31: 1453-1457Crossref PubMed Scopus (31) Google Scholar Although episodes of capsule switching have been reported in countries using vaccines against serogroup C,10Alcalá B Arreaza L Salcedo C Uría MJ De La Fuente L Vázquez JA Capsule switching among C:2b:P1.2,5 meningococcal epidemic strains after mass immunization campaign, Spain.Emerg Infect Dis. 2002; 8: 1512-1514Crossref PubMed Scopus (48) Google Scholar, 11Pérez-Trallero E Vicente D Montes M Cisterna R Positive effect of meningococcal C vaccination on serogroup replacement in Neisseria meningitidis.Lancet. 2002; 360: 953Summary Full Text Full Text PDF PubMed Scopus (41) Google Scholar these episodes were generally not widespread or lasting. Nevertheless, because experience of elimination of serogroup A by glycoconjugate vaccines is limited, and capsule replacement was also shown for other bacteria including pneumococci,12Scott JR Millar EV Lipsitch M et al.Impact of more than a decade of pneumococcal conjugate vaccine use on carriage and invasive potential in Native American communities.J Infect Dis. 2012; 205: 280-288Crossref PubMed Scopus (87) Google Scholar the establishment of surveillance systems needs to be prioritised. Further research should focus on the development and validation of serological correlates of protection and on the establishment of improved methods for detection of carriage,9Greenwood B Priorities for research on meningococcal disease and the impact of serogroup A vaccination in the African meningitis belt.Vaccine. 2013; 31: 1453-1457Crossref PubMed Scopus (31) Google Scholar because exact duration of protection and age-stratified carriage prevalences are needed for the identification of optimum vaccination strategies.13Tartof S Cohn A Tarbangdo F et al.Identifying optimal vaccination strategies for Serogroup A Neisseria meningitidis conjugate vaccine in the African meningitis belt.PLoS One. 2013; 8: e63605Crossref PubMed Scopus (31) Google Scholar Although the paper by Daugla and colleagues1Daugla DM Gami JP Gamougam K et al.Effect of a serogroup A meningococcal conjugate vaccine (PsA–TT) on serogroup A meningococcal meningitis and carriage in Chad: a community trial.Lancet. 2013; (published online Sept 12.)http://dx.doi.org/10.1016/S0140-6736(13)61612-8PubMed Google Scholar represents an important milestone in the battle against meningococcal disease, many more mysteries regarding meningococci await clarification; thus, the jury remains out as to why serogroup A, prevalent in the northern hemisphere until the 1980s, has mostly disappeared from Europe,14Kriz P Wieffer H Holl K Rosenlund M Budhia S Vyse A Changing epidemiology of meningococcal disease in Europe from the mid-20th to the early 21st Century.Expert Rev Vaccines. 2011; 10: 1477-1486Crossref PubMed Scopus (27) Google Scholar and why, with a few ephemeral exceptions,15Jones DM Sutcliffe EM Group A meningococcal disease in England associated with the Haj.J Infect. 1990; 21: 21-25Summary Full Text PDF PubMed Scopus (38) Google Scholar it has not been successfully reintroduced into industrialised countries despite frequent travel. I have received honoraria for talks from Novartis Vaccines and Diagnostics, GlaxoSmithKline, and Baxter. Effect of a serogroup A meningococcal conjugate vaccine (PsA–TT) on serogroup A meningococcal meningitis and carriage in Chad: a community studyPSA–TT was highly effective at prevention of serogroup A invasive meningococcal disease and carriage in Chad. How long this protection will persist needs to be established. Full-Text PDF Open Access