Evaluation of meningococcal meningitis vaccination strategies for the meningitis belt in Africa

Initial validation of a simulation model for estimating the impact of serogroup A Neisseria meningitidis vaccination in the African meningitis belt

We previously developed a mathematical simulation of serogroup A Neisseria meningitidis (NmA) transmission in Burkina Faso, with the goal of forecasting the relative benefit of different vaccination programs. Here, we revisit key structural assumptions of the model by comparing how accurately the different assumptions reproduce observed NmA trends following vaccine introduction. A priori, we updated several of the model's parameters based on recently published studies. We simulated NmA disease under different assumptions about duration of vaccine-induced protection (including the possibility that vaccine-induced protection may last longer than natural immunity). We compared simulated and observed case counts from 2011-2017. We then used the best-fit model to forecast the impact of different vaccination strategies. Our updated model, with the assumption that vaccine-induced immunity lasts longer than immunity following NmA colonization, was able to reproduce observed trends in NmA disease. The updated model predicts that, following a mass campaign among persons 1-29 years of age, either routine immunization of 9 month-old children or periodic mini-campaigns among children 1-4 years of age will lead to sustained control of epidemic NmA in Burkina Faso. This validated model can help public health officials set policies for meningococcal vaccination in Africa.

Estimating costs of care for meningitis infections in low- and middle-income countries

Meningitis infections are often associated with high mortality and risk of sequelae. The costs of treatment and care for meningitis are a great burden on health care systems, particularly in resource-limited settings. The objective of this study is to review data on the costs of care for meningitis in low- and middle-income countries, as well as to show how results could be extrapolated to countries without sound data. We conducted a systematic review of the literature from six databases to identify studies examining the cost of care in low- and middle-income countries for all age groups with suspected, probable, or confirmed meningitis. We extracted data on treatment costs and sequelae by infectious agent and/or pathogen, where possible. Using multiple regression analysis, a relationship between hospital costs and associated determinants was investigated in order to predict costs in countries with missing data. This relationship was used to predict treatment costs for all 144 low- and middle-income countries. The methodology of conducting a systematic review, extrapolating, and setting up a standard database can be used as a tool to inform cost-effectiveness analyses in situations where cost of care data are poor. Both acute and long-term costs of meningitis could be extrapolated to countries without reliable data. Although only bacterial causes of meningitis can be vaccine-preventable, a better understanding of the treatment costs for meningitis is crucial for low- and middle-income countries to assess the cost-effectiveness of proposed interventions in their country. This cost information will be important as inputs in future cost-effectiveness studies, particularly for vaccines.

From Epidemic Meningitis Vaccines for Africa to the Meningitis Vaccine Project

BACKGROUND

Polysaccharide vaccines had been used to control African meningitis epidemics for >30 years but with little or modest success, largely because of logistical problems in the implementation of reactive vaccination campaigns that are begun after epidemics are under way. After the major group A meningococcal meningitis epidemics in 1996-1997 (250,000 cases and 25,000 deaths), African ministers of health declared the prevention of meningitis a high priority and asked the World Health Organization (WHO) for help in developing better immunization strategies to eliminate meningitis epidemics in Africa.

METHODS

WHO accepted the challenge and created a project called Epidemic Meningitis Vaccines for Africa (EVA) that served as an organizational framework for external consultants, PATH, the US Centers for Disease Control and Prevention (CDC), and the Bill & Melinda Gates Foundation (BMGF). Consultations were initiated with major vaccine manufacturers. EVA commissioned a costing study/business plan for the development of new group A or A/C conjugate vaccines and explored the feasibility of developing these products as a public-private partnership. Representatives from African countries were consulted. They confirmed that the development of conjugate vaccines was a priority and provided information on preferred product characteristics. In parallel, a strategy for successful introduction was also anticipated and discussed.

RESULTS

The expert consultations recommended that a group A meningococcal conjugate vaccine be developed and introduced into the African meningitis belt. The results of the costing study indicated that the "cost of goods" to develop a group A - containing conjugate vaccine in the United States would be in the range of US$0.35-$1.35 per dose, depending on composition (A vs A/C), number of doses/vials, and presentation. Following an invitation from BMGF, a proposal was submitted in the spring of 2001.

CONCLUSIONS

In June 2001, BMGF awarded a grant of US$70 million to create the Meningitis Vaccine Project (MVP) as a partnership between PATH and WHO, with the specific goal of developing an affordable MenA conjugate vaccine to eliminate MenA meningitis epidemics in Africa. EVA is an example of the use of WHO as an important convening instrument to facilitate new approaches to address major public health problems.

Global practices of meningococcal vaccine use and impact on invasive disease

A number of countries now include meningococcal vaccines in their routine immunization programs. This review focuses on different approaches to including meningococcal vaccines in country programs across the world and their effect on the burden of invasive meningococcal disease (IMD) as reflected by pre and post-vaccine incidence rates in the last 20 years. Mass campaigns using conjugated meningococcal vaccines have lead to control of serogroup C meningococcal disease in the UK, Canada, Australia, Spain, Belgium, Ireland, and Iceland. Serogroup B disease, predominant in New Zealand, has been dramatically decreased, partly due to the introduction of an outer membrane vesicle (OMV) vaccine. Polysaccharide vaccines were used in high risk people in Saudi Arabia and Syria and in routine immunization in China and Egypt. The highest incidence region of the meningitis belt initiated vaccination with the serogroup A conjugate vaccine in 2010 and catch-up vaccination is ongoing. Overall results of this vaccine introduction are encouraging especially in countries with a moderate to high level of endemic disease. Continued surveillance is required to monitor effectiveness in countries that recently implemented these programs.

Meningococcal conjugate vaccines: optimizing global impact

Meningococcal conjugate vaccines have several advantages over polysaccharide vaccines, including the ability to induce greater antibody persistence, avidity, immunologic memory, and herd immunity. Since 1999, meningococcal conjugate vaccine programs have been established across the globe. Many of these vaccination programs have resulted in significant decline in meningococcal disease in several countries. Recent introduction of serogroup A conjugate vaccine in Africa offers the potential to eliminate meningococcal disease as a public health problem in Africa. However, the duration of immune response and the development of widespread herd immunity in the population remain important questions for meningococcal vaccine programs. Because of the unique epidemiology of meningococcal disease around the world, the optimal vaccination strategy for long-term disease prevention will vary by country.

Meningococcal factor H binding proteins in epidemic strains from Africa: implications for vaccine development

BACKGROUND

Factor H binding protein (fHbp) is an important antigen for vaccines against meningococcal serogroup B disease. The protein binds human factor H (fH), which enables the bacteria to resist serum bactericidal activity. Little is known about the vaccine-potential of fHbp for control of meningococcal epidemics in Africa, which typically are caused by non-group B strains.

METHODOLOGY/PRINCIPAL FINDINGS

We investigated genes encoding fHbp in 106 serogroup A, W-135 and X case isolates from 17 African countries. We determined complement-mediated bactericidal activity of antisera from mice immunized with recombinant fHbp vaccines, or a prototype native outer membrane vesicle (NOMV) vaccine from a serogroup B mutant strain with over-expressed fHbp. Eighty-six of the isolates (81%) had one of four prevalent fHbp sequence variants, ID 4/5 (serogroup A isolates), 9 (W-135), or 74 (X) in variant group 1, or ID 22/23 (W-135) in variant group 2. More than one-third of serogroup A isolates and two-thirds of W-135 isolates tested had low fHbp expression while all X isolates tested had intermediate or high expression. Antisera to the recombinant fHbp vaccines were generally bactericidal only against isolates with fHbp sequence variants that closely matched the respective vaccine ID. Low fHbp expression also contributed to resistance to anti-fHbp bactericidal activity. In contrast to the recombinant vaccines, the NOMV fHbp ID 1 vaccine elicited broad anti-fHbp bactericidal activity, and the antibodies had greater ability to inhibit binding of fH to fHbp than antibodies elicited by the control recombinant fHbp ID 1 vaccine.

CONCLUSION/SIGNIFICANCE

NOMV vaccines from mutants with increased fHbp expression elicit an antibody repertoire with greater bactericidal activity than recombinant fHbp vaccines. NOMV vaccines are promising for prevention of meningococcal disease in Africa and could be used to supplement coverage conferred by a serogroup A polysaccharide-protein conjugate vaccine recently introduced in some sub-Saharan countries.

A hypothetical explanatory model for meningococcal meningitis in the African meningitis belt

Despite much progress in surveillance and biological research, no explanation exists to date for the epidemic pattern of meningitis in the African meningitis belt, which is required to mathematically model the impact of vaccine strategies or to predict epidemics. This paper presents a hypothetical explanatory model for epidemic meningococcal meningitis. Four incidence patterns are defined as model states, including endemic incidence during the rainy season, ubiquitous hyperendemicity during the dry season, occasional localized epidemics, and-at the regional level-regular epidemic waves spanning over communities or years. While the transition from endemic to hyperendemic situation in a community is caused by an increase in risk of meningitis given colonization by a virulent meningococcus (due to damage of the pharyngeal mucosa by dry climate), the transition from hyperendemic to epidemic situation involves increased pharyngeal colonization and transmission (possibly caused by viral respiratory infection epidemics). The described mechanisms are sufficient to explain the 10- to 100-fold incidence increase that both transitions usually imply. Epidemic waves occur if new meningococcal strains which escape pre-existing immunity, enter the population. Future research should include the impact of viral co-infection on bacterial colonization and invasion.

Meningococcal factor H-binding protein variants expressed by epidemic capsular group A, W-135, and X strains from Africa

BACKGROUND

Meningococcal epidemics in Africa are generally caused by capsular group A strains, but W-135 or X strains also cause epidemics in this region. Factor H-binding protein (fHbp) is a novel antigen being investigated for use in group B vaccines. Little is known about fHbp in strains from other capsular groups.

METHODS

We investigated fHbp in 35 group A, W-135, and X strains from Africa.

RESULTS

The 22 group A isolates, which included each of the sequence types (STs) responsible for epidemics since 1963, and 4 group X and 3 group W-135 isolates from recent epidemics had genes encoding fHbp in antigenic variant group 1. The remaining 6 W-135 isolates had fHbp variant 2. Within each fHbp variant group, there was 92%-100% amino acid identity, and the proteins expressed conserved epitopes recognized by bactericidal monoclonal antibodies. Serum samples obtained from mice vaccinated with native outer membrane vesicle vaccines from mutants engineered to express fHbp variants had broad bactericidal activity against group A, W-135, or X strains.

CONCLUSIONS

Despite extensive natural exposure of the African population, fHbp is conserved among African strains. A native outer membrane vesicle vaccine that expresses fHbp variants can potentially elicit protective antibodies against strains from all capsular groups that cause epidemics in the region.

Meningococcal meningitis in Mali: a long-term study of persistence and spread

OBJECTIVES

Meningococcal meningitis (MM) is still a huge threat in the African meningitis belt. To fight against epidemics, a strengthened health information system, based upon weekly collected data, was set up in Mali. We aimed to study the spatio-temporal dynamics of MM in this country between 1992 and 2003.

METHODS

We were first interested in the impact of population size on the disease persistence. We then used cross-correlation analysis to study the spread of the disease on three different spatial scales, i.e., inter-region (global) and inter-district and intra-district (local) levels.

RESULTS

We found no persistence of MM at district level in Mali during the whole of the study period. However, we found persistence on a nationwide scale after the 1997 big epidemics, as opposed to the 1992-1996 time periods. In terms of spread, two main regions seem to lead MM dynamics in Mali, even if on a local scale the 'cities-villages' diffusion pattern was not systematically observed.

CONCLUSIONS

This study improves knowledge on the spread and persistence of MM in Mali in recent years. It constitutes a first spatial study describing persistence and spread of MM in an African meningitis belt country. The next step should be the integration of vaccination and genetic variability data to clarify the route of spread of the disease in the human population.

Safety, immunogenicity, and antibody persistence of a new meningococcal group A conjugate vaccine in healthy Indian adults

We performed a double-blind, randomized, controlled phase I study to assess safety, immunogenicity, and antibody persistence of the new meningococcal group A conjugate vaccine (PsA-TT) in healthy volunteers aged 18-35 years. Of the 74 male subjects enrolled, 24 received the PsA-TT vaccine (Group 1), 25 received the Meningococcal Polysaccharide Vaccine A+C, Pasteur, Lyon, France (Group 2), and 25 received the Tetanus Toxoid Vaccine Adsorbed, SIIL, Pune India (Group 3). No immediate reactions were observed. Local and systemic solicited reactions within 7 days post-vaccination and unsolicited adverse events (AEs) were mild and similar among the three groups and resolved without sequelae. No serious AEs were notified up to 1 year post-vaccination. Four weeks post-vaccination, a slightly higher proportion of Group 1 subjects had a four-fold increase in SBA titers compared to Group 2 subjects (83% versus 72%, p>0.05). SBA GMTs in Groups 2 and 3 were higher than in Group 3 (p<0.05). Serogroup A-specific IgG GMCs were significantly higher in Group 1 than in Groups 2 (p<0.05) and 3 (p<0.05). After 1 year SBA titers were significantly higher in Group 1 than in Group 2 (p<0.05). The new PsA-TT vaccine was shown to be safe, immunogenic, and able to elicit persistent functional antibody titers in adults. This opens the prospective for further development and licensure of this vaccine to eliminate epidemic meningitis in sub-Saharan Africa.

Comparative study of meningitis dynamics across nine African countries: a global perspective

Background

Meningococcal meningitis (MM) represents an important public health problem especially in the "meningitis belt" in Africa. Although seasonality of epidemics is well known with outbreaks usually starting in the dry season, pluri-annual cycles are still less understood and even studied. In this context, we aimed at study MM cases time series across 9 sahelo-sudanian countries to detect pluri-annual periodicity and determine or not synchrony between dynamics. This global and comparative approach allows a better understanding of MM evolution in time and space in the long-term.

Results

We used the most adapted mathematical tool to time series analyses, the wavelet method. We showed that, despite a strong consensus on the existence of a global pluri-annual cycle of MM epidemics, it is not the case. Indeed, even if a clear cycle is detected in all countries, these cycles are not as permanent and regular as generally admitted since many years. Moreover, no global synchrony was detected although many countries seemed correlated.

Conclusion

These results of the first large-scale study of MM dynamics highlight the strong interest and the necessity of a global survey of MM in order to be able to predict and prevent large epidemics by adapted vaccination strategy. International cooperation in Public Health and cross-disciplines studies are highly recommended to hope controlling this infectious disease.

Burden of invasive disease caused by Haemophilus influenzae type b in Bamako, Mali: impetus for routine infant immunization with conjugate vaccine

BACKGROUND

Population-based, bacteriologically confirmed disease burden data aid decision makers in African countries pondering whether to introduce Haemophilus influenzae type b (Hib) immunization for infants.

METHODS

A bacteriology laboratory was established in Hopital Gabriel Toure, serving Bamako, Mali. Children age 0-15 years with fever > or =39 degrees C or syndromes compatible with invasive bacterial disease (meningitis, etc.) were eligible. From 2 to 5 mL of blood or relevant body fluid were inoculated into Bactec Ped Plus/F medium for automated culture; body fluids were also inoculated directly onto solid media. Hib was confirmed by standard microbiologic techniques and antibiograms generated by disk diffusion.

RESULTS

From June 1, 2002 to May 31, 2004, 3592 (87.8%) of 4092 children admitted to Hopital Gabriel Toure with high fever or suspected invasive bacterial disease were cultured, including 1745 who were 0-11 months old, 1132 who were 1-4 years old and 715 who were 5-15 years old. Hib was isolated from 207 Bamako children, 81 from blood alone and 124 from cerebrospinal fluid (with or without positive blood culture). Of 207 cases 204 (98.5%) occurred in children younger than age 5 years (annual incidence, 45.2/10) and 159 (77%) in infants age 0-11 months (annual incidence, 158.4/10). Peak incidence (370.0 cases/10) and 12 of 21 Hib deaths occurred in 6- to 7-month-olds. Of the Hib isolates, 11.1% were resistant to ampicillin, 32% to chloramphenicol and 0.5% to ceftriaxone.

CONCLUSIONS

The substantial burden of invasive Hib disease documented in Bamako has prompted the Malian government to introduce routine infant immunization with Hib conjugate.

Polysaccharide vaccines for preventing serogroup A meningococcal meningitis

BACKGROUND

Randomised trials carried out over two decades ago showed that the polysaccharide vaccine prevented serogroup A meningococcal meningitis. Subsequent non-randomised studies, however, suggested significant variations in the age-specific duration of protection among young children.

OBJECTIVES

The aim of the review was to determine the effect of polysaccharide serogroup A vaccine for preventing serogroup A meningococcal meningitis. The specific objectives were to assess the age-specific effects of the vaccine, the effect of booster doses in children under five years of age, and the duration of protection in children and adults.

SEARCH STRATEGY

In 2004, the review was updated. The following databases were searched for records of new trials: the Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library Issue 4, 2004); MEDLINE (January 1966 to November Week 1 2004); and EMBASE (January 1990 to September 2004).

SELECTION CRITERIA

The first stage of the review included randomised trials. The second stage included non- randomised studies that addressed specific outcomes not answered by the randomised trials.

DATA COLLECTION AND ANALYSIS

One reviewer assessed the methodological quality of the randomised trials and two reviewers independently identified and assessed the non-randomised studies. Of the twelve eligible Randomized trials, four were excluded because of the high risk of bias in assessing vaccine efficacy. Data from the trials were pooled using the Exact method to assess vaccine efficacy at one, two and three years post vaccination. Of the 15 non-randomised studies, only two addressed the specific objectives not answered by the randomised trials but were assessed to be at high risk of bias.

MAIN RESULTS

The protective effect within the first year of vaccination was consistent across the randomised trials, and the summary vaccine efficacy was 95% (95% confidence interval (CI) 87% to 99%). Protection extended into the second and third year after vaccination but the results did not attain statistical significance. The vaccine was protective in Finnish children aged 3 months to five years. The latter was also the only trial that assessed the effect of a booster dose in children under two years of age but lacked power to yield statistically significant results. The vaccine was protective in one- to five-year old children in developing countries (Nigeria and Sudan) but the age-specific efficacy in strata between one and five years of age could not be determined.

AUTHORS' CONCLUSIONS

For the first year after vaccination, the polysaccharide serogroup A vaccine was strongly protective against serogroup A meningococcal meningitis in participants over five years of age. It was also protective beyond the first year after vaccination in this age group but the level of vaccine efficacy could not be determined with precision. Children aged one to five years in developing countries were also protected but the level of efficacy in this age group could not be determined. While the vaccine was strongly protective among children aged three months to five years in developed countries the level of efficacy across age strata within this age group could not be determined. The number of children aged under two years was too small to draw conclusions on the protective effect of a booster dose of vaccine.

Meningococcal vaccines

Meningococcal disease is one of the most feared and serious infections in the young and its prevention by vaccination is an important goal. The high degree of antigenic variability of the organism makes the meningococcus a challenging target for vaccine prevention. Meningococcal polysaccharide vaccines against serogroup A and C are efficacious and have been widely used, often in combination with serogroup Y and W135 components. Their relative lack of immunogenicity in young children and infants can be overcome by conjugation to a protein carrier. The effectiveness of serogroup C glycoconjugate vaccines in children of all ages has been demonstrated and they have now been introduced into routine vaccination schedules. Conjugate vaccines against other serogroups, including A, Y, and W135 will soon be available and it is hoped they may emulate this success. Prevention of serogroup B disease has proven more elusive. Several serogroup B vaccines based on outer membrane vesicles have been shown to be immunogenic and reasonably effective in adults and older children, but the protection offered by them is chiefly strain-specific. Multivalent recombinant PorA vaccines have been developed to broaden the protective effect, but no efficacy data are available as yet. Intensive efforts have been directed at other outer membrane protein vaccine candidates and lipopolysaccharide, and some of these have been shown to offer protection in experimental animal models. Nonpathogenic Neisseriae spp. such as Neisseria lactamica are also possible vaccine candidates. Previously unknown proteins have been identified from in silico analysis of the meningococcal genome and their vaccine potential explored. However, none of these has yet been presented as the 'universal' protective antigen and work in this field continues to be held back by our limited knowledge concerning the mechanisms of natural protection against serogroup B meningococci.

Bacterial Meningitis in Burkina Faso: Surveillance Using Field-Based Polymerase Chain Reaction Testing

BACKGROUND

In addition to frequent epidemics of group A meningococcal disease, endemic bacterial meningitis due mostly to Neisseria meningitidis, pneumococcus, and Haemophilus influenzae type b is a serious problem in sub-Saharan Africa. The improved ability to identify the etiologic agent in cases of bacterial meningitis will facilitate more rapid administration of precise therapy.

METHODS

To describe the epidemiology of bacterial meningitis and evaluate the usefulness of field-based polymerase chain reaction (PCR) testing, we implemented population-based meningitis surveillance in Burkina Faso during 2002-2003 by use of PCR, culture, and antigen detection tests.

RESULTS

Among persons aged 1 month to 67 years, the incidences of meningococcal meningitis, pneumococcal meningitis, and Haemophilus influenzae type b meningitis were 19 cases (n=179), 17 cases (n=162), and 7.1 cases (n=68) per 100,000 persons per year, respectively. Of the cases of meningococcal meningitis, 72% were due to N. meningitidis serogroup W135. Pneumococcal meningitis caused 61% of deaths and occurred in a seasonal pattern that was similar to that of meningococcal meningitis. Of cases of pneumococcal meningitis and N. meningitidis serogroup W135 meningitis, 71% occurred among persons >2 years of age. Most patients, regardless of the etiology of their illness and the existence of an epidemic, received short-course therapy with oily chloramphenicol. Compared with culture as the gold standard, the sensitivity and specificity of PCR in the field were high; this result was confirmed in Burkina Faso and Paris.

CONCLUSIONS

Precise and rapid identification of etiologic agents is critical for improvement in the treatment and prevention of meningitis, and, thus, PCR should be considered for wider use in Africa. Vaccines against Streptococcus pneumoniae, N. meningitidis (including serogroup W135), and H. influenzae type b all will have a major impact on the bacterial meningitis burden. Antibiotic recommendations need to consider the importance of S. pneumoniae, even during the epidemic season.

Serum group a anticapsular antibodies in a Sudanese population immunized with meningococcal polysaccharide vaccine during a group A epidemic

BACKGROUND

Vaccination during group A meningococcal epidemics is reported to decrease the number of new cases of disease. However, implementing mass vaccination is often delayed, and little information is available on whether immunity increases in a population vaccinated during an epidemic when exposure to the epidemic strain is common.

METHODS

A convenience sample of 134 previously unimmunized persons, ages 3-49 years, were immunized with a meningococcal polysaccharide vaccine. Their serum group A antibody responses were compared with those of 26 adults immunized in California with no known group A exposure.

RESULTS

Before immunization, serum anticapsular antibody concentrations were 10-fold higher in Sudanese adults and 4-fold higher in Sudanese, ages 3-17 years, than in North American adults (geometric means, 29 and 13 microg/ml, respectively, versus 3 microg/ml, P < 0.001). Seventy-five percent of the Sudanese had serum bactericidal titers that correlate with protection (> or 1/128). Nearly all Sudanese with low bactericidal titers before vaccination developed protective bactericidal antibody responses after vaccination, and the magnitude of the anticapsular antibody responses of the Sudanese was similar to that of the immunized North Americans.

INTERPRETATION

The high titers of naturally acquired antibody in the Sudanese may reflect widespread exposure to the epidemic strain and underscore difficulties of instituting immunization before exposure occurs. Also epidemics in sub-Saharan Africans may not abate even if 75% of the population is immune to disease as long as the organism is transmitted widely among both immune and susceptible persons.

Vaccines against bacterial meningitis

Meningitis remains an important cause of morbidity and mortality among children >5 years of age and is especially prevalent in developing countries. Effective routine immunization against Hib, pneumococcus and serogroupC meningococcus has had a significant impact on both invasive disease and carriage caused by these encapsulated bacteria. The major challenge in prevention of meningitis remains the delivery of vaccines worldwide, especially to resource-poor regions with the greatest disease burden.

Serogroup W-135 meningococcal disease during the Hajj, 2000

An outbreak of serogroup W-135 meningococcal disease occurred during the 2000 Hajj in Saudi Arabia. Disease was reported worldwide in Hajj pilgrims and their close contacts; however, most cases were identified in Saudi Arabia. Trends in Saudi meningococcal disease were evaluated and the epidemiology of Saudi cases from this outbreak described. Saudi national meningococcal disease incidence data for 1990 to 2000 were reviewed; cases from January 24 to June 5, 2000, were retrospectively reviewed. The 2000 Hajj outbreak consisted of distinct serogroup A and serogroup W-135 outbreaks. Of 253 identified cases in Saudi Arabia, 161 (64%) had serogroup identification; serogroups W-135 and A caused 93 (37%) and 60 (24%) cases with attack rates of 9 and 6 cases per 100,000 population, respectively. The 2000 Hajj outbreak was the first large serogroup W-135 meningococcal disease outbreak identified worldwide. Enhanced surveillance for serogroup W-135, especially in Africa, is essential to control this emerging epidemic disease.

A season of aseptic meningitis in Germany: epidemiologic, clinical and diagnostic aspects

OBJECTIVE

We assessed epidemiologic, clinical and laboratory features of aseptic meningitis during one season of multiserotype enteroviral meningitis in East Germany in 70 consecutive patients with aseptic meningitis admitted to the Children's University Hospital Leipzig.

RESULTS

Patients, age 1 to 16 years, typically presented with headache, emesis and fever, whereas signs of meningeal irritation were only moderately expressed in one-half of the patients. The median number of leukocytes in the CSF was 151 cells/mm(3) (range, 2 to 1,820) with a high percentage of polymorphonuclear cells (PMNs). Initial blood counts showed mild leukocytosis and pronounced PMN predominance (78.9 +/- 1.3%). The percentage of PMNs in the peripheral blood decreased in favor of mononuclear cells after 3 days to a pattern more compatible with viral infection as opposed to that suggestive for bacteria in the beginning. Mean cerebrospinal fluid values of protein, glucose and lactate and the C-reactive protein were mildly elevated or normal. Nonpolio enteroviruses were detected in 30 of 70 patients. Subsequent serotyping revealed echovirus type 13 (13 patients), type 6 (2), type 30 (1) and coxsackie B virus type 5 (2). There were no differences in demographic or clinical data between enterovirus positive and negative patients.

CONCLUSIONS

Even though individual laboratory values do not solely allow discrimination between viral and bacterial meningitis, the combined epidemiologic, clinical and laboratory data facilitate the diagnosis of aseptic meningitis in most cases. Viral diagnostics, identifying echovirus type 13 that thus far has not been associated with epidemics of meningitis, adds important epidemiologic information.

Development of vaccines against meningococcal disease

Neisseria meningitidis is a major cause of bacterial meningitis and sepsis. Polysaccharide-protein conjugate vaccines for prevention of group C disease have been licensed in Europe. Such vaccines for prevention of disease caused by groups A (which is associated with the greatest disease burden worldwide), Y, and W135 are being developed. However, conventional approaches to develop a vaccine for group B strains, which are responsible for most cases in Europe and the USA, have been largely unsuccessful. Capsular polysaccharide-based vaccines can elicit autoantibodies to host polysialic acid, whereas the ability of most non-capsular antigens to elicit broad-based immunity is limited by their antigenic diversity. Many new membrane proteins have been discovered during analyses of genomic sequencing data. These antigens are highly conserved and, in mice, elicit serum bactericidal antibodies, which are the serological hallmark of protective immunity in man. Therefore, there are many promising new vaccine candidates, and improved prospects for development of a broadly protective vaccine for group B disease, and for control of all meningococcal disease.

Timely detection of meningococcal meningitis epidemics in Africa

BACKGROUND

Epidemics of meningococcal disease in Africa are commonly detected too late to prevent many cases. We assessed weekly meningitis incidence as a tool to detect epidemics in time to implement mass vaccination.

METHODS

Meningitis incidence for 41 subdistricts in Mali was determined from cases recorded in health centres (1989-98) and from surveillance data (1996-98). For incidence thresholds of 5 to 20 cases per 100000 inhabitants per week, we calculated sensitivity and specificity for detecting epidemics, and determined the time lapse between threshold and epidemic peak.

FINDINGS

We recorded 9084 meningitis cases. Clinic-based weekly incidence of 5 and 10 cases per 100000 inhabitants detected all meningitis epidemics (sensitivity 100%, 95% CI 93-100), with median threshold-to-peak time of 5 and 3 weeks. Under-reporting reduced sensitivity: only surveillance thresholds of 5 or 7 cases per 100000 inhabitants per week detected all epidemics. Crossing the lower threshold before the 10th calendar week doubled epidemic risk relative to crossing it later (relative risk 2.1, 95% CI 1.4-3.2). At 10 cases per 100000 inhabitants per week, specificity for outbreak prediction was 88%, 95% CI 83-91). For populations under 30000, 3 to 5 cases in one or two weeks predicted epidemics with 85% to 97% specificity.

INTERPRETATION

Low meningitis thresholds improve timely detection of epidemics. Ten cases per 100000 inhabitants per week in one area confirm epidemic activity in a region, with few false alarms. An alert threshold of 5 cases per 100000 inhabitants per week allows time to investigate, prepare for an epidemic, and initiate mass vaccination where appropriate. For populations under 30000, the alert threshold is two cases in a week. High quality surveillance is essential.

Comparison of cost-effectiveness of preventive and reactive mass immunization campaigns against meningococcal meningitis in West Africa: a theoretical modeling analysis

For epidemic meningitis control in sub-Saharan Africa, the World Health Organization recommends a strategy of emergency vaccination with meningococcal A + C polysaccharide vaccine when epidemic thresholds are exceeded. An alternative strategy for areas without effective surveillance systems is mass preventive campaigns before outbreaks occur. A model was formulated to simulate epidemics and to compare the cost-effectiveness of these two strategies for the district of Matam, Senegal, where an actual preventive campaign was performed during 1997. The preventive strategy prevented 59% of the cases compared to 49% for the emergency strategy. The cost per case prevented was US$59 for the preventive strategy and US$133 for the reactive strategy, and the preventive strategy saved US$0.20 per habitant. Preventive meningococcal vaccination through mass campaigns prevented more outcomes at a lower cost, provided that the occurrence of an epidemic could be predicted within 3 years and that the vaccination coverage rates for the preventive and standard strategies were > 70% and < 94%, respectively. Sub-Saharan African countries without effective surveillance systems should consider mass preventive campaigns while awaiting an affordable conjugate vaccine.

Polysaccharide vaccines for preventing serogroup A meningococcal meningitis

BACKGROUND

Controlled trials over two decades ago showed that the polysaccharide vaccine prevented meningococcal meningitis. Subsequent observational studies suggested variations in the level and duration of protection, particularly among young children.

OBJECTIVES

To determine the effect of polysaccharide serogroup A vaccine for preventing serogroup A meningococcal meningitis.

SEARCH STRATEGY

MEDLINE and the Cochrane Controlled Trials Register.

SELECTION CRITERIA

Randomised and other prospective controlled trials.

DATA COLLECTION AND ANALYSIS

One reviewer collected data and assessed the methodologic quality of the trials. Data were pooled using the Exact method to assess vaccine efficacy at one, two and three years post-vaccination.

MAIN RESULTS

The protective effect within the first year was consistent across all eight trials, including one with participants exclusively under six years of age (in Finland); overall vaccine efficacy was 95% (Exact 95% CI 87%, 99%). The Finnish trial lacked statistical power to assess the effect of a booster dose given to children less than 18 months old. In the three other trials that included children less than six years old (one in Sudan and two in Nigeria), none of the vaccinated children developed meningitis, but the statistical significance of this finding was undetermined. Protection extended into the second (in two studies) and third (in one study) years after vaccination, but these results were also not statistically significant.

REVIEWER'S CONCLUSIONS

When compared with current recommendations, the methodological quality and relative incompleteness of the published reports could arguably render the trials invalid for this review. However, it was unlikely that the results of the trials in such diverse settings would have been biased towards a strong and consistent protective effect. Immunogenicity trials were not included in this review. Stage two of the review will assess the vaccine effect from observational studies.