International Health Advance Access published April 15, 2015
Int Health doi:10.1093/inthealth/ihv025
Meningococcal meningitis: vaccination outbreak response and epidemiological changes in the African meningitis belt Francisco Javier Carod Artal* Neurology Department, Raigmore hospital, Old Perth road, Inverness, IV2 3UJ, UK and Universitat Internacional de Cataluya (UIC), Barcelona, Spain *Corresponding author: Tel: +44 1463706229; E-mail: [email protected]
Received 23 February 2015; revised 25 March 2015; accepted 25 March 2015 The main approach to controlling epidemics of meningococcal meningitis in the African meningitis belt has been reactive vaccination campaigns with serogroup A polysaccharide vaccine once the outbreak reached an incidence threshold. Early reactive vaccination is effective in reducing morbidity and mortality. A recent paper in International Health has shown that earlier reactive vaccination campaigns may be even more effective than increasing the coverage area of vaccination. Monovalent serogroup A conjugate vaccine programs have recently been launched to prevent transmission in endemic areas in the African meningitis belt. Conjugate vaccines can induce immunological memory and have impact on pharyngeal carriage. However, reactive vaccination still has a role to play taking into account the dynamic changes in the epidemiology of meningitis in this area. Keywords: Conjugate vaccine, Meningitis surveillance, Neisseria meningitides, Polysaccharide vaccine, Serogroup A, Vaccination outbreak response
The epidemiology of meningococcal meningitis in the African meningitis belt is characterized by a high baseline incidence, seasonal annual outbreaks and intermittent explosive epidemics.1 Epidemic meningococcal disease in sub-Saharan countries has occurred as large outbreaks every few years since the last century. Epidemics have been reported in Ghana, Nigeria, Sudan, Burkina Fasso, Chad and Niger, among other countries. Large outbreaks have resulted in the occurrence of tens of thousands of cases and thousands of deaths, affected mostly older children and young adults and severely disrupted the health services of these poor countries.1,2 Serogroup A has been dominant in the meningitis belt since the early twentieth century, and epidemics usually occur during the dry season. However, outbreaks caused by serogroups C, W and X have also been reported. Serogroup W was responsible for outbreaks in Burkina Fasso (2002), Niger (2010–2011) and Guinea (2013), and serogroup X also caused outbreaks in Ghana and Kenya (2005) and Niger (2006).2–4 Meningococcal meningitis incidence during epidemics have been estimated in 1000–1200 per 100 000 inhabitants, whereas reported incidence during non-epidemic seasons may vary between 10 and 20 cases per 100 000 inhabitants. Invasive disease has been associated with a case fatality rate of around 5–10% and approximately 10–20% of patients suffering meningococcal meningitis have severe neurological sequel including learning disability, epilepsy, hemiparesis and deafness. The high fatality rate and severity of sequel also provoke long-term economic impact on the households of those affected. Treatments may also result in signiﬁcant healthcare costs in resource-poor settings.
Meningococcal disease, although debilitating, is considered a preventable illness, and vaccination strategies have been implemented.5 The relevance of the meningitis vaccination response worldwide is high, and in Africa I would say essential. Control of meningococcal epidemics in the African meningitis belt classically rely upon reactive vaccination campaigns once incident cases pass an incidence threshold.6 Early reactive vaccination campaigns with polysaccharide vaccine have saved many lives. Recently in International Health, Ferrari et al.7 quantiﬁed the impact of meningitis vaccination in Katsina state, Nigeria in 2009 during the large outbreak that resulted in more than 75 000 cases and 4000 deaths. Although the overall impact of the vaccination campaign ranged from 4 to 12%, at local level cases were reduced by 50% when vaccination was done early in the epidemic. It is well known that polysaccharide vaccines induce only shortterm immunity in children, have no impact on carriage and have not reduced the frequency of meningococcal epidemics. However, the epidemiology of meningococcal meningitis may have changed recently after the introduction of polysaccharide/protein conjugate vaccine in the region.5 Conjugate vaccines are more likely to prevent epidemics than polysaccharide vaccines because they are immunogenic in young children, induce immunological memory and prevent or decrease pharyngeal carriage. In Europe and North America, meningococcal serogroup C conjugate vaccines reduced and almost eliminated serogroup C meningitis and carriage.8 In the last few years, a monovalent serogroup A conjugate vaccine (MenAfriVac) was developed by the Meningitis Vaccine Project.
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Since 2010, mass vaccination programs with the conjugate vaccine were launched in the African meningitis belt. Subjects aged 1–29 years were vaccinated, and serogroup A meningococcal disease and carriage was reduced in Burkina Fasso, Mali, Niger, Chad and other countries. No meningitis cases due to serogroup A were detected in Burkina Fasso the next year following the vaccination campaign. The serogroup A meningococcal conjugate vaccine seems to be immunogenic and safe, confers individual protection and herd immunity. Indeed, a 94% difference in crude incidence of meningitis was observed in areas with mass vaccination. Changes in the frequency of meningococcal serogroups are expected after the introduction of conjugate vaccination, and in South Africa, serogroup W has replaced serogroup A as dominant. Nevertheless, reactive campaigns with polysaccharide vaccine will be still necessary to control meningitis outbreaks in the African belt. Active surveillance programs are needed as spread of virulent strains may be facilitated by travel and pilgrimage. Recent outbreaks due to a novel C strain have been reported in Sokoto State, Nigeria, in 2013, and in the adjacent state in 2014 and 2015.3 Although active surveillance of meningococcal disease was implemented in many sub-Saharan countries, the accuracy of the local health systems to early detect meningococcal epidemics is still a weak point. The need for active and enhanced surveillance in African countries at risk of meningococcal epidemics has been recently identiﬁed as the highest priority.9 Research to determine the duration of the protection against serogroup A meningococcal disease provided by the conjugate vaccine is also another research top priority in Africa. Ferrari et al.7 showed that reactive vaccination with polysaccharide vaccine during meningococcal meningitis outbreaks can signiﬁcantly reduce the case burden when conducted early. In their model, early vaccination campaigns were predicted to be more effective than the alternative strategy of increasing the vaccination coverage. In the stroke ﬁeld, time to thrombolysis means brain. Timely response in vaccination reactive campaigns can prevent people being afﬂicted by neurological sequel of meningitis. However, delays in the surveillance and reporting system, vaccine availability and logistics may limit the timely strategy. The epidemiological pattern has changed after the introduction of MenAfriVac, and an increase in the number of cases due to X serogroup has been reported. WHO recently reviewed the strategy for intervention in the African meningitis belt and emphasized the timeliness of response.10 WHO recommended that vaccination campaigns be implemented as soon as possible, and within 4 weeks of crossing the epidemic threshold.10 Epidemic thresholds to initiate treatment and vaccination response have also been reviewed. They have been deﬁned as 10 cases/100 000 in a week for population of 30 000– 100 000; and 5 cases in a week or a doubling of incidence in a 3-week period for population of