GEO Meningitis Environmental Risk Consultative Meeting, 26-27 sept 2007, WHO, Geneva

Project :Long-term epidemiology of Meningococcal Meningitis in the

African belt: dynamics and impact of vaccination

Spatio-temporal dynamics (spread, persistence, periodicity),

Comparative approach, impact of vaccination

Hélène Broutin, PhDPost-doctoral researcher

(Supervisor: Dr Mark A. Miller)

Division of International Epidemiology and Population Studies,Fogarty International Center,National Institutes of Health

GEO Meningitis Environmental Risk Consultative Meeting, 26-27 sept 2007, WHO, Geneva

- For which population size does the disease persist in time ?

- Can we identify sources of infection (does a same locality or district constantly suffer first cases of an epidemic ?)

- Do we observe similar routes of transmission of the disease in all countries ?

- Do we observe synchrony of epidemics between countries ? Do we observe regular waves of cases ?

Idea = studying the past (long time series) and comparing dynamics in order to:

- detect global patterns vs specialty

- understand the impact of vaccination

- be able to suggest adapted vaccination strategies

Better mechanistic understanding of the epidemiology of MM during recent decades (emergence, diffusion, persistence)

Questions and goals …

Metapopulation

=POPULATION of POPULATIONS

CONNECTED BY MIGRATIONS

Concepts when Ecology meets Epidemiology…

concept cities /villages

IMPACT of VACCINATION ?

Ecology

=> POPULATION SIZEPERSISTENCE

SPREAD

=> POPULATION FLUX

Epidemiology

Critical Community Size (CCS)

- DIFFUSION : concept cities / villages = diseases spread from big cities to villages[Anderson R.M. & May R.M, 1991; Grenfell B.T. & Bolker B.M., 1998]

- PERSISTANCE : Critical Community Size (CCS) =the minimal population size below which a disease cannot persist in a susceptible population without external input(s)

[Bartlett M.S., 1957; Black F.L., 1966; Anderson R.M. & May R.M., 1991; Grenfell B.T. & Harwood J., 1997]

Concepts when Ecology meets Epidemiology…

analyses of time-period of disease extinction (period with no new cases in a locality) in relation with the population size

Cases time series analyses between localities

Population dynamics(Extinction-recolonization concept)

extinction risk for the species

Species maintain

Concepts when Ecology meets Epidemiology…

Best control

Disease persistence

Population dynamics and Epidemiology (Periodicities - synchronism)

Concepts when Ecology meets Epidemiology…

These questions are also highly relevant in a global control perspective

GEO Meningitis Environmental Risk Consultative Meeting, 26-27 sept 2007, WHO, Geneva

LOCAL–SCALE

(intra – district)

Persistence / Diffusion in relation with population size : can we detect sources of infection ?

GLOBAL –SCALE

NATIONAL SCALE(inter-district)

- Periodicity / synchrony

Mali

Sikasso District

Spatio-temporal dynamics of MM in Africa

Not only considered epidemics periods (e.g.1994 and 1996) but also inter-epidemics (i.e. 1993 to 1996) to make the link between epidemics)

GEO Meningitis Environmental Risk Consultative Meeting, 26-27 sept 2007, WHO, Geneva

Illustrations …

A) B)

Figure extracted from Broutin H, Mantilla-Breniers N. and P. Rohani , Ecology of infectious disease:an example with two vaccine-preventable infectious diseases. Chapt 12 In ‘Encyclopediae of infectious diseases”, in press

GEO Meningitis Environmental Risk Consultative Meeting, 26-27 sept 2007, WHO, Geneva

Detailed and long epidemiological time

series :

Weekly, by district

Genetics data (serotype)

Vaccination data

ALL THESE analyses will allow a BETTER comprehension in order to be able to Model dynamics of the disease

- local persistence of the disease in a long-term

- local to global diffusion patterns of MM

- comparison between countries

Data

- spatial and temporal persistence of serotype in population

- periodicity and route of transmission of different serotypes?

- quantifying lags between serotypes dynamics

Different steps …

Data analyses

- impact of vaccination on these dynamics

GEO Meningitis Environmental Risk Consultative Meeting, 26-27 sept 2007, WHO, Geneva

Integration of all components …

Population size

Genotype

Vaccine status

Climate

Limits / questions

Last of immunity ?

Proportion of asymptomatic carrier?

GEO Meningitis Environmental Risk Consultative Meeting, 26-27 sept 2007, WHO, Geneva

- Collaboration with Dr MP. Préziosi from the WHO (Vaccine Program Initiative)

- Dr Pejman Rohani, University of Georgia, Athens, GA, USA.

Availability of detailed data: on MM cases, vaccination and serotype, weekly data, for different countries….

Thank you for your attention