Modelling the effect of changes in vaccine effectiveness and transmission contact rates on pertussis epidemiology

PESCO P; BERGERO P; FABRICIUS G; HOZBOR D

Epidemics

elsevier

Año: 2014

1755-4365

The incidence of the highly infectious respiratory disease named pertussis or whooping cough hasbeen increasing for the past two decades in different countries, as in much of the highly vaccinatedworld. A decrease in vaccine effectiveness over time, especially when acellular vaccines were usedfor primary doses and boosters, and pathogen adaptation to the immunity conferred by vaccineshave been proposed as possible causes of the resurgence. The contributions of these factors are notexpected to be the same in different communities, and this could lead to different epidemiologicaltrends. In fact, differences in the magnitude and dynamics of pertussis outbreaks as well as in thedistribution of notified cases by age have been reported in various regions.Using an age-structured mathematical model designed by us, we evaluated how the changes insome of the parameters that could be related to the above proposed causes of disease resurgence ?vaccine effectiveness and effective transmission rates ? may impact on pertussis transmission.When a linear decrease in vaccine effectiveness (VE) was assayed, a sustained increase in pertussisincidence was detected mainly in infants and children. On the other hand, when changes in effectivetransmission rates (βij) were made, a dynamic effect evidenced by the presence of large peaksfollowed by deep valleys was detected. In this case, greater incidence in adolescents than inchildren was observed. These different trends in the disease dynamics due to modifications in VE orβij were verified in 18 possible scenarios that represent different epidemiological situations.Interestingly we found that both incidence trends produced by the model and their age distributionresemble the profiles obtained from data reported in several regions. The implications of thesecorrelations are discussed.