Mathematical Modeling of pertussis transmission: evaluating the impact of delayed vaccination in infants

G. FABRICIUS; P. PESCO; P. BERGERO; D. HOZBOR

Erice

Workshop; "Mathematical and Computational Epidemiology of Infectious diseases - the interplay between models and public health policies" 65th Conference of the International School of Mathematics "G. Stampacchia".; 2015

ETTORE MAJORANA FOUNDATION AND CENTRE FOR SCIENTIFIC CULTURE

The incidence of the highly contagious respiratory disease namedpertussis or whooping cough has been increasing for the past two decades inseveral countries despite the highly extended vaccination. The reasons for thisresurgence are a matter of discussion and, while trying to understand thiscomplex problem, new strategies that include more boosters for adolescents andadults have been adopted in many countries in an attempt to improve the controlof the disease. However, the impact of these measures on infants (the risk agegroup) is not clear. In this context mathematical models are being increasinglyused to study the disease transmission and to estimate the impact of differentcontrol strategies. In previous work, we developed an age structured deterministicmathematical model with 9 epidemiological classes to evaluate the effect of anadolescent booster on pertussis infant incidence [1]. We have also applied themodel to explore different possible causes for pertussis resurgence that arecompatible with observed epidemiological data [2].  In this contribution,recent improvements introduced into the model to evaluate the effect of delaysin the administration of the first three vaccination doses are described. Themethodology involves the consideration of additional epidemiological classes tokeep track of the number of doses administered to the population independentlyof their immune status [3]. Using data gathered from vaccination centers inurban and suburban areas in an Argentine city, we evaluated the impact oninfant incidence of reducing the observed delays in vaccineadministration. We conclude that reducing delays in vaccination orimproving the coverage of the first doses are measures with a high potentialimpact on the risk age group, clearly higher than the inclusion of anadolescent or adult booster at a given age. Robustness of the results waschecked for different sets of parameters representing different possibleepidemiological scenarios. [1] "Modeling pertussis transmission to evaluate the effectivenessof an adolescent booster in Argentina". G.Fabricius, P.Bergero, M.Ormazabal, A.Maltz and D. Hozbor. Epidemiology and Infection 141,718-734 (2013).[2] "Modelling the effect of changes in vaccine effectiveness andtransmission contact rates on pertussis epidemiology".  P. Pesco, P.Bergero, G. Fabriciusand D. Hozbor. Epidemics 7, 13-21 (2014).[3] "Mathematical modeling of delayed pertussis vaccination ininfants". P. Pesco, P.Bergero, G. Fabriciusand D. Hozbor.  Accepted for publication in Vaccine on 1stJuly 2015.