A deterministic epidemiology model to study pertussis in Argentina

G. FABRICIUS; A: LODEIRO; A. MELGAREJO; A. GRAIEB; D. HOZBOR

Bruselas

Conferencia; 27th Annual Meeting of the European Society for Paediatric Infectious Disease; 2009

European Society for Paediatric Infectious Disease

 Background and aims: Vaccination against pertussis started in Argentina in the 70s, coverage being estimated as 90% in average. Despite this, disease incidence is rising, registering a 6-fold increase since 2002. Though a clear increase is observed at all age groups, children <6 months old had the highest proportion of cases. In this age group a delay in vaccine application was registered: around 30% of infants had fewer vaccine doses than they should. To estimate how this delay may contribute to the observed increase in disease incidence, an epidemiological model was used. Methods: Starting from a SIR-type model we introduced the age-dependent vaccination scheme currently employed in Argentina. The model contains 9 epidemiological classes and 30 age groups. Parameters were taken from literature and local epidemiological data. Results: We followed a deterministic approach. The steady state was reached by allowing temporal system evolution to constancy of all age epidemiological class sizes. Delay in vaccine application was simulated by modifying the coverage rates of each dose. By setting vaccine efficacy in 90% for all doses, the model estimates that a delay in the first vaccination comparable to that observed caused a 12% increment in infected individuals aged 0-2 year-old. This value went to 22% by simulating such delay also in the second and third doses. If non-uniform vaccine efficacy were considered for each dose the relative impacts changed. Conclusions: Based on mathematical model analysis, a delay in vaccine application might be related with the observed disease incidence increase.