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  • A 5-year Chlamydia vaccination programme could reverse disease-related koala population decline: Predictions from a mathematical model using field data

    Author(s)
    Craig, Andrew P
    Hanger, Jon
    Loader, Jo
    Ellis, William AH
    Callaghan, John
    Dexter, Cathryn
    Jones, Darryl
    Beagley, Kenneth W
    Timms, Peter
    Wilson, David P
    Griffith University Author(s)
    Jones, Darryl N.
    Year published
    2014
    Metadata
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    Abstract
    Background Many koala populations around Australia are in serious decline, with a substantial component of this decline in some Southeast Queensland populations attributed to the impact of Chlamydia. A Chlamydia vaccine for koalas is in development and has shown promise in early trials. This study contributes to implementation preparedness by simulating vaccination strategies designed to reverse population decline and by identifying which age and sex category it would be most effective to target. Methods We used field data to inform the development and parameterisation of an individual-based stochastic simulation model of ...
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    Background Many koala populations around Australia are in serious decline, with a substantial component of this decline in some Southeast Queensland populations attributed to the impact of Chlamydia. A Chlamydia vaccine for koalas is in development and has shown promise in early trials. This study contributes to implementation preparedness by simulating vaccination strategies designed to reverse population decline and by identifying which age and sex category it would be most effective to target. Methods We used field data to inform the development and parameterisation of an individual-based stochastic simulation model of a koala population endemic with Chlamydia. The model took into account transmission, morbidity and mortality caused by Chlamydia infections. We calibrated the model to characteristics of typical Southeast Queensland koala populations. As there is uncertainty about the effectiveness of the vaccine in real-world settings, a variety of potential vaccine efficacies, half-lives and dosing schedules were simulated. Results Assuming other threats remain constant, it is expected that current population declines could be reversed in around 5-6 years if female koalas aged 1-2 years are targeted, average vaccine protective efficacy is 75%, and vaccine coverage is around 10% per year. At lower vaccine efficacies the immunological effects of boosting become important: at 45% vaccine efficacy population decline is predicted to reverse in 6 years under optimistic boosting assumptions but in 9 years under pessimistic boosting assumptions. Terminating a successful vaccination programme at 5 years would lead to a rise in Chlamydia prevalence towards pre-vaccination levels. Conclusion For a range of vaccine efficacy levels it is projected that population decline due to endemic Chlamydia can be reversed under realistic dosing schedules, potentially in just 5 years. However, a vaccination programme might need to continue indefinitely in order to maintain Chlamydia prevalence at a sufficiently low level for population growth to continue.
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    Journal Title
    Vaccine
    Volume
    32
    DOI
    https://doi.org/10.1016/j.vaccine.2014.05.049
    Subject
    Biological sciences
    Other biological sciences not elsewhere classified
    Agricultural, veterinary and food sciences
    Biomedical and clinical sciences
    Publication URI
    http://hdl.handle.net/10072/66329
    Collection
    • Journal articles

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