Unintended Consequences and the Paradox of Control: Management of Emerging Pathogens with Age-Specific Virulence

Abstract

We project the long term incidence of Zika virus disease (ZVD) under varying hazards of infection and consider how the age-distribution of disease burden varies between these scenarios. Pathogens with age-structured disease outcomes, such as rubella and Zika virus, require that management decisions consider their impact not only on total disease incidence but also on distribution of disease burden within a population. In some cases, reductions of overall transmission can have the paradoxical effect of increasing the incidence of severe disease despite decreasing the total incidence. This happens because of corresponding increases in the average age of infection. Beginning with the current population structure and demographic rates of Brazil, we project forward total ZVD burden as measured by cases occurring inpregnant women and document the scenarios under which a paradox of control for Zika management emerges. We conclude that while a paradox of control can occurfor ZVD, the higher total costs from increasing the average age of infection will only be realized after several decades and vanish under conservative discounting of future costs. This indicates that managers faced with an emerging pathogen should prioritize current disease incidence over potential increases in severe disease outcomes in the endemic state.