Modelling heterogeneity and the impact of chemotherapy and vaccination against human hookworm

There is a growing emphasis on the development of vaccines against helminths (worms), and mathematical models provide a useful tool to assess the impact of new vaccines under a range of scenarios. The present study describes a stochastic individual-based model to assess the relative impact of chemotherapy and vaccination against human hookworm infection and investigates the implications of potential correlations between risk of infection and vaccine efficacy. Vaccination is simulated as a reduction in susceptibility to infection and the model includes population heterogeneities and dynamical waning of protection. To help identify appropriate measures of vaccine impact, we present a novel framework to quantify the vaccine impact on the infection-associated morbidity and introduce a measure of symmetry to study the correspondence between reduction in intensity and reduction in morbidity. Our modelling shows that, in high-transmission settings, the greatest impact of vaccination will be attained when vaccine efficacy is the greatest among individuals harbouring the heaviest worm burdens, and that the decline of morbidity primarily depends on the level of protection attained in the most at risk 8–12% of the population. We also demonstrate that if risk of infection and vaccine protection are correlated, there is not always a direct correspondence between the reduction in worm burden and in morbidity, with the precise relationship varying according to transmission setting

An empirical analysis of the retention of dissatisfied business services customers using structural equation modelling

This study extends the body of literature concerning service switching, complaint handling, dependence and commitment by investigating why dissatisfied B2B customers do not switch service providers. Specifically, it develops and tests a social exchange-based model examining how dissatisfied, but behaviourally loyal, customers act in terms of their repurchase intentions. A conceptual model, specifying a set of hypothesised relationships between dimensions of switching costs, interpersonal relationships, dimensions of complaint handling, satisfaction with complaint handling, attractiveness of alternatives, dependence, calculative commitment and repurchase intentions, was examined using AMOS 17.0 on a sample of 376 business directors/managers from responding organisations. The results show that satisfaction with complaint handling, benefit-loss costs, dependence and calculative commitment significantly increase customers’ repurchase intentions. The findings also indicate that dependence, interpersonal relationships and specific types of switching costs influence customers’ calculative commitment, and the latter influences intentions to repurchase services. The study builds on the Investment Model by including justice components, and examines the effects of different types of antecedents on calculative commitment that have previously not been examined