Modelling Management for the Maintenance of Measles Elimination
Open Access
- Author:
- Mckee, Amalie Elena
- Graduate Program:
- Biology
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- August 16, 2016
- Committee Members:
- Katriona Shea, Dissertation Advisor/Co-Advisor
Andrew Fraser Read, Committee Chair/Co-Chair
Matthew Joseph Ferrari, Committee Member
Ottar N Bjornstad, Committee Member
Rachel Annette Smith, Outside Member - Keywords:
- measles
routine immunization
vaccine policy
disease elimination
mathematical models
modelling management - Abstract:
- Despite decades of extensive control, measles remains a major contributor to vaccine-preventable childhood death. As such, measles is an important target for global eradication. Global eradication comprises two parts; achieving local elimination, and maintaining local elimination while elimination is achieved elsewhere. This dissertation focuses on the post measles elimination context, which requires high levels of population immunity to be maintained via a carefully considered vaccine policy. Vaccine policies for measles typically contain combinations of two basic vaccine strategies; routine immunization and supplemental immunization activities (SIAs). Routine immunization consists of one or more doses administered to children at specified target ages. SIAs are campaigns that typically take place over a wide geographic area, where all children within a specified target age range are vaccinated within a relatively short time. In my work I examine the interaction of human demographic structure, maternal immunity, and three health system factors (coverage, age targets, and correlation between populations receiving each dose) on the effectiveness of a vaccine strategy for the maintenance of measles elimination. I find that, regardless of health system aspects, maternal immunity and age structure can interact so that measles elimination is impossible to maintain with a single dose routine immunization strategy. When a second dose is added, the maximum level of population immunity maintainable in a population still depends on demographic structure, but age target selection can ensure that measles elimination is sustained. The optimal age target for each of two doses of routine immunization depends on the coverage of the other dose as well as on demographic structure. Low correlation between the populations receiving each dose increases the proportion of the population that receives at least one dose, thereby increasing population immunity, at the cost of increasing the rate of primary vaccine failure. The effect of correlation may outweigh the effects of age structure and changing coverage in a variety of real contexts. The dependence of population immunity on the correlation between doses also arises when SIAs are administered in conjunction with the second routine dose. Whether or not the second dose contributes more to population immunity than SIAs depends, not just on the coverage of all doses, but also on their correlation. While population immunity is important for maintaining elimination, optimal age target selection depends on a carefully specified objective; the optimal age targets to minimize the incidence or mortality of a reintroduction outbreak are different. I conclude with a synthesis of my research in the context of previous measles work. Overall, I show that, while coverage is essential, human demography, maternal immunity, and other aspects of the health system (coverage, age targets and correlation) also have significant effects on population immunity, and hence the maintenance of measles elimination.