The potential impact of immunization campaign budget re-allocation on global eradication of paediatric infectious diseases.

Tiffany Fitzpatrick,Chris T Bauch

doi:10.1186/1471-2458-11-739

Abstract

BackgroundThe potential benefits of coordinating infectious disease eradication programs that use campaigns such as supplementary immunization activities (SIAs) should not be over-looked. One example of a coordinated approach is an adaptive "sequential strategy": first, all annual SIA budget is dedicated to the eradication of a single infectious disease; once that disease is eradicated, the annual SIA budget is re-focussed on eradicating a second disease, etc. Herd immunity suggests that a sequential strategy may eradicate several infectious diseases faster than a non-adaptive "simultaneous strategy" of dividing annual budget equally among eradication programs for those diseases. However, mathematical modeling is required to understand the potential extent of this effect.MethodsOur objective was to illustrate how budget allocation strategies can interact with the nonlinear nature of disease transmission to determine time to eradication of several infectious diseases under different budget allocation strategies. Using a mathematical transmission model, we analyzed three hypothetical vaccine-preventable infectious diseases in three different countries. A central decision-maker can distribute funding among SIA programs for these three diseases according to either a sequential strategy or a simultaneous strategy. We explored the time to eradication under these two strategies under a range of scenarios.ResultsFor a certain range of annual budgets, all three diseases can be eradicated relatively quickly under the sequential strategy, whereas eradication never occurs under the simultaneous strategy. However, moderate changes to total SIA budget, SIA frequency, order of eradication, or funding disruptions can create disproportionately large differences in the time and budget required for eradication under the sequential strategy. We find that the predicted time to eradication can be very sensitive to small differences in the rate of case importation between the countries. We also find that the time to eradication of all three diseases is not necessarily lowest when the least transmissible disease is targeted first.ConclusionsRelatively modest differences in budget allocation strategies in the near-term can result in surprisingly large long-term differences in time required to eradicate, as a result of the amplifying effects of herd immunity and the nonlinearities of disease transmission. More sophisticated versions of such models may be useful to large international donors or other organizations as a planning or portfolio optimization tool, where choices must be made regarding how much funding to dedicate to different infectious disease eradication efforts.

Highlights

The potential benefits of coordinating infectious disease eradication programs that use campaigns such as supplementary immunization activities (SIAs) should not be over-looked
While polio has been successfully eradicated from the western hemisphere, it remains endemic in four countries (Nigeria, Afghanistan, India, and Pakistan) [4]
We compared a “simultaneous strategy” of dividing the budget among SIA programs each year for the three diseases to a “sequential strategy” where all annual SIA budget is first allocated to Disease A until Disease A is eradicated, at which point all annual SIA budget is redirected to Disease B until it is eradicated, and to Disease C until it is eradicated

Summary

Introduction

The potential benefits of coordinating infectious disease eradication programs that use campaigns such as supplementary immunization activities (SIAs) should not be over-looked. Vaccine-preventable paediatric infectious diseases such as polio, measles and pertussis continue to cause significant morbidity and mortality worldwide. An estimated 1 in 200 polio infections lead to irreversible paralysis and 5-10% of these individuals will die due to breathing complications resulting from this paralysis [5,6]. Headache, fatigue and vomiting [7] Some of these initial symptoms are similar to those of common ailments such as influenza, making infection control difficult. Pertussis (whooping cough) infection is most serious in infants under 6 months of age: 1 in 200 of these infants will die as a result of complications, such as brain damage [6,10]. Symptoms at this stage closely resemble those of a common cold, meaning a person may not notice they are infected with pertussis, and can unknowingly transmit the pathogen [12]

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