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Meningitis outbreaks and vaccination strategy
F Varaine1, D A Caugant, J Y Riou
1WHO Collaborating Centre for Reference and Research on Meningococci, National Institute of Public Health, Oslo, Norway.
Abstract:
Three outbreaks of meningitis caused by Neisseria meningitidis serogroup A (subgroup III) are described: Niger (1991), Burundi (1992), and Guinea (1993). These outbreaks showed unusual characteristics: a shorter inter-epidemic interval (Niger), unusual geographical location outside the meningitis belt (Burundi and Guinea), and high age-specific attack rates in all age groups (Burundi and Guinea). Mass immunization campaigns mobilized considerable human and financial means (US $322,000 and 3000 person-days of work for health personnel to immunize 629,000 people in Guinea). The vaccination coverage was over 80% in densely populated areas (Burundi and urban Guinea), but below 50% in less populated areas (24/27 and 26/30 sub-districts in Niger and Guinea, respectively). The preventive fraction (proportion of cases prevented by vaccination) was substantial in Guinea (35% for a vaccine efficacy of 85%) and was higher where the campaign was initiated earlier. An 'alert' threshold indicating the onset of an epidemic of 15/100,000 cases in one week showed good sensitivity (94%), specificity (98%) and positive predictive value (89%) in Burundi, permitting quick decision making outside the meningitis belt. These 3 meningococcal meningitis outbreaks show the need for epidemic emergency preparedness and for vigilance on the whole African continent.
Insights
Three Neisseria meningitidis meningitis outbreaks in Africa revealed unusual patterns and highlighted the need for preparedness. Mass immunization campaigns showed variable success, emphasizing the importance of early detection and response strategies.
Area of Science:
- Epidemiology
- Infectious Diseases
- Public Health
Background:
- Describes three Neisseria meningitidis serogroup A outbreaks in Niger (1991), Burundi (1992), and Guinea (1993).
- Highlights unusual outbreak characteristics: shorter inter-epidemic intervals, atypical geographical locations, and high attack rates across all age groups.
Purpose of the Study:
- To analyze the characteristics of these Neisseria meningitidis outbreaks.
- To evaluate the effectiveness of mass immunization campaigns and early warning systems.
Main Methods:
- Retrospective analysis of outbreak data from Niger, Burundi, and Guinea.
- Assessment of vaccination coverage and preventive fraction.
- Evaluation of an 'alert' threshold for epidemic detection.
Main Results:
- Mass immunization campaigns achieved over 80% coverage in dense areas but less than 50% in sparse regions.
- Substantial preventive fraction (35%) observed in Guinea with 85% vaccine efficacy.
- An 'alert' threshold demonstrated high sensitivity (94%) and specificity (98%) for epidemic detection in Burundi.
Conclusions:
- Outbreaks of Neisseria meningitidis meningitis exhibit evolving patterns requiring enhanced surveillance.
- Effective epidemic preparedness and rapid response are crucial across the African continent.
- Early detection systems and targeted vaccination strategies are vital for controlling meningococcal meningitis.