[Detection of meningococcal meningitis epidemics in Africa: a new recommendation]

In sub-Saharan Africa, the control of meningococcal meningitis epidemics relies on early epidemic detection and mass vaccination. However, experience shows that interventions are often initiated too late to have a significant impact on the epidemic. A new recommendation drafted by participants of a consensus meeting proposes an alert threshold and an epidemic threshold based on the weekly number or incidence of meningitis cases, according to the population size and the epidemic risk, resulting in indicators with high sensitivity and specificity for the detection of an emerging epidemic. Meningitis outbreak investigations must include an assessment of the quality of epidemiologic surveillance. The new recommendation is published in English and French in the Weekly Epidemiologic Record [12]. The success of this consensus meeting shows the value of integrating results from surveillance, field experience and operational research for designing new health strategies.

Surveillance for meningococcal disease and strategies for use of conjugate meningococcal vaccines in the United States

BACKGROUND

Neisseria meningitidis is a leading cause of bacterial meningitis in US; new capsular type-specific conjugate vaccines offer an opportunity for improved control of meningococcal disease. We evaluated the relative burdens of invasive meningococcal disease in US and examined the projected impact of various meningococcal conjugate vaccination strategies on rates of meningococcal disease.

METHODS

Meningococcal disease incidence rates were determined from active, population-based surveillance in selected US areas. Models were created to determine impact of vaccination of infants, toddlers, adolescents or college students with meningococcal conjugate vaccines, with assumptions for vaccine coverage, efficacy and duration of protection. Although we examined possible conjugate vaccine formulations including serogroups A, C, Y and W-135, the final vaccine impact analysis excluded serogroups A and W-135. Outcome measures were cumulative meningococcal disease incidence, and incidence 10 years after initiating vaccination among 0-22-year-olds.

RESULTS

In models of serogroup C+Y meningococcal conjugate vaccination of infants, toddlers and adolescents, the cumulative incidence of meningococcal disease was reduced by 54, 48 and 25%, respectively; the toddler strategy had the greatest impact per dose. After 10 years of routine meningococcal conjugate vaccination, meningococcal disease could be reduced by 50% and deaths by 64%.

CONCLUSIONS

Use of meningococcal conjugate vaccine could markedly reduce meningococcal disease incidence. Our data, along with vaccine formulation and vaccination program considerations, will be important in determining the optimal choice of vaccination strategy.

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

BACKGROUND

Although the meningococcal polysaccharide vaccine has contributed to the control of Group A meningitis in the "meningitis belt" of Africa, recurrent large outbreaks have led to questions regarding vaccination strategy. We evaluated current and hypothetical vaccination strategies for the region.

METHODS

A model was formulated to analyze the effectiveness and costs of vaccine campaigns in response to outbreaks based on 7 years of weekly incidence data from Burkina Faso. Additional models analyzed the potential impact and costs of either a 1- or 4-dose routine scheduled delivery of meningococcal polysaccharide vaccine based on data reported to the World Health Organization from 16 countries during 1948 through 1996. Vaccine efficacy, vaccination coverage and economic data from literature reviews provided model assumptions.

RESULTS

For Burkina Faso neither 1- nor 4-dose vaccination schedules would prevent >30% of meningitis cases compared with the 42% prevented through an outbreak response program of vaccinating districts, which reach an incidence of 15 per 100000 persons for 2 weeks. For the entire meningitis belt, routine coverage with the 1- or 4-dose schedule meningococcal vaccine would require 4.9 and 19.6 million doses annually, respectively, for an annual net cost of $4.4 to $12.3 million and prevent an average 10300 to 12600 cases (23 to 28%), assuming a long term vaccine efficacy of 50%. In addition an initial "catch-up" campaign costing up to $72 million to vaccinate the population from 1 to 30 years of age would be required before achieving that level of effectiveness.

CONCLUSION

Given the relatively poor routine vaccination coverage in this region, current strategies of vaccination campaigns that achieve higher coverage would generally be more effective and less costly than the modeled routine scheduled programs, assuming that campaigns can be rapidly implemented. Until a better vaccine is available, countries in this region would be more efficient in improving the response times to outbreaks, perhaps through improved surveillance, and in bolstering existing vaccination infrastructures rather than embarking on strategies of questionable effectiveness.

Cleavase fragment length polymorphism analysis of Neisseria meningitidis basic metabolic genes

Cleavase fragment length polymorphism (CFLP) is a subtyping system based on the property of the enzyme cleavase to recognize junctions between single- and double-stranded regions of DNA formed after denaturation and cooling. To assess the capacity of CFLP for discriminating Neisseria meningitidis serogroup B strains belonging to the electrophoretic type (ET) 5 (ET-5) complex from other serogroup B strains, 30 serogroup B N. meningitidis isolates were subtyped by CFLP with internal fragments of five housekeeping genes, adk, aspC, carA, dhp, and glnA. Two genes (glnA and carA) which demonstrated a high degree of diversity for the serogroup B isolates were then used to further evaluate the suitability of CFLP for screening 50 serogroup C N. meningitidis outbreak-associated and sporadic-case isolates with a single metabolic gene. The results were compared to those from multilocus enzyme electrophoresis (MEE), the current standard subtyping method. CFLP was able to distinguish the ET-5 complex isolates from other serogroup B isolates as efficiently as MEE. Furthermore, CFLP analysis of a single gene was sufficient to identify and cluster the serogroup C isolates belonging to the ET-37 complex from other, unrelated serogroup C isolates but was not capable of differentiating between the isolates of the major individual ETs of this complex (ET-17 and ET-24) causing most serogroup C meningococcal disease outbreaks in the United States. CFLP based on a single gene with a high degree of diversity but not under selective pressure can be applied to the rapid screening of a large number of isolates related to the recognized epidemic complex ET-5 or ET-37. Additionally, CFLP can be used as an initial screening tool to survey the amount of diversity in genes that might be used to develop a DNA sequence-based subtyping system.

Efficacy of meningococcal vaccine and barriers to vaccination

CONTEXT

Use of the quadrivalent meningococcal vaccine for control of outbreaks has increased in recent years, but the efficacy of meningococcal vaccine during mass vaccination campaigns in US civilian populations has not been assessed.

OBJECTIVES

To evaluate the efficacy of the quadrivalent meningococcal vaccine against serogroup C meningococcal disease in a community outbreak setting and to evaluate potentially modifiable barriers to vaccination in an area with persistent meningococcal disease following immunization.

DESIGN

Matched case-control study of vaccine efficacy using cases of serogroup C meningococcal disease in persons eligible for vaccination during mass vaccination campaigns. Control patients were matched by neighborhood and age. The control group was used to identify possible barriers to vaccination.

SETTING

Gregg County, Texas, population 106076, from 1993 to 1995.

PARTICIPANTS

A total of 17 case patients with serogroup C meningococcal disease eligible for vaccine and 84 control patients.

MAIN OUTCOME MEASURES

Vaccine efficacy and risk factors associated with nonvaccination.

RESULTS

Vaccine efficacy among 2- to 29-year-olds was 85% (95% confidence interval, 27%-97%) and did not change in bivariate analyses with other risk factors that were significant in univariate analysis. Among control patients, older age was strongly associated with nonvaccination; vaccination rates for 2- to 4-year-olds, 5- to 18-year-olds, and 19- to 29-year-olds were 67%, 48%, and 20%, respectively (chi2 for linear trend, P=.01).

CONCLUSIONS

The meningococcal polysaccharide vaccine was effective against serogroup C meningococcal disease in this community outbreak. Although specific barriers to vaccination were not identified, older age was a risk factor for nonvaccination in the target population of 2- to 29-year-olds. In future outbreaks, emphasis should be placed on achieving high vaccination coverage, with special efforts to vaccinate young adults.