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Demographics, epidemiology and the impact of vaccination campaigns in a measles-free world – Can elimination be maintained?

INTRODUCTION: All six WHO regions currently have goals for measles elimination by 2020. Measles vaccination is delivered via routine immunization programmes, which in most sub-Saharan African countries reach children around 9 months of age, and supplementary immunization activities (SIAs), which tar...

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Autores principales: Prada, J.M., Metcalf, C.J.E., Takahashi, S., Lessler, J., Tatem, A.J., Ferrari, M.
Formato: Online Artículo Texto
Lenguaje:English
Publicado: Elsevier Science 2017
Materias:
Acceso en línea:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5341736/
https://www.ncbi.nlm.nih.gov/pubmed/28216186
http://dx.doi.org/10.1016/j.vaccine.2017.02.008
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author Prada, J.M.
Metcalf, C.J.E.
Takahashi, S.
Lessler, J.
Tatem, A.J.
Ferrari, M.
author_facet Prada, J.M.
Metcalf, C.J.E.
Takahashi, S.
Lessler, J.
Tatem, A.J.
Ferrari, M.
author_sort Prada, J.M.
collection PubMed
description INTRODUCTION: All six WHO regions currently have goals for measles elimination by 2020. Measles vaccination is delivered via routine immunization programmes, which in most sub-Saharan African countries reach children around 9 months of age, and supplementary immunization activities (SIAs), which target a wider age range at multi-annual intervals. In the absence of endemic measles circulation, the proportion of individuals susceptible to measles will gradually increase through accumulation of new unvaccinated individuals in each birth cohort, increasing the risk of an epidemic. The impact of SIAs and the financial investment they require, depend on coverage and target age range. MATERIALS AND METHODS: We evaluated the impact of target population age range for periodic SIAs, evaluating outcomes for two different levels of coverage, using a demographic and epidemiological model adapted to reflect populations in 4 sub-Saharan African countries. RESULTS: We found that a single SIA can maintain elimination over short time-scales, even with low routine coverage. However, maintaining elimination for more than a few years is difficult, even with large (high coverage/wide age range) recurrent SIAs, due to the build-up of susceptible individuals. Across the demographic and vaccination contexts investigated, expanding SIAs to target individuals over 10 years did not significantly reduce outbreak risk. CONCLUSIONS: Elimination was not maintained in the contexts we evaluated without a second opportunity for vaccination. In the absence of an expanded routine program, SIAs provide a powerful option for providing this second dose. We show that a single high coverage SIA can deliver most key benefits in terms of maintaining elimination, with follow-up campaigns potentially requiring smaller investments. This makes post-campaign evaluation of coverage increasingly relevant to correctly assess future outbreak risk.
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spelling pubmed-53417362017-03-13 Demographics, epidemiology and the impact of vaccination campaigns in a measles-free world – Can elimination be maintained? Prada, J.M. Metcalf, C.J.E. Takahashi, S. Lessler, J. Tatem, A.J. Ferrari, M. Vaccine Article INTRODUCTION: All six WHO regions currently have goals for measles elimination by 2020. Measles vaccination is delivered via routine immunization programmes, which in most sub-Saharan African countries reach children around 9 months of age, and supplementary immunization activities (SIAs), which target a wider age range at multi-annual intervals. In the absence of endemic measles circulation, the proportion of individuals susceptible to measles will gradually increase through accumulation of new unvaccinated individuals in each birth cohort, increasing the risk of an epidemic. The impact of SIAs and the financial investment they require, depend on coverage and target age range. MATERIALS AND METHODS: We evaluated the impact of target population age range for periodic SIAs, evaluating outcomes for two different levels of coverage, using a demographic and epidemiological model adapted to reflect populations in 4 sub-Saharan African countries. RESULTS: We found that a single SIA can maintain elimination over short time-scales, even with low routine coverage. However, maintaining elimination for more than a few years is difficult, even with large (high coverage/wide age range) recurrent SIAs, due to the build-up of susceptible individuals. Across the demographic and vaccination contexts investigated, expanding SIAs to target individuals over 10 years did not significantly reduce outbreak risk. CONCLUSIONS: Elimination was not maintained in the contexts we evaluated without a second opportunity for vaccination. In the absence of an expanded routine program, SIAs provide a powerful option for providing this second dose. We show that a single high coverage SIA can deliver most key benefits in terms of maintaining elimination, with follow-up campaigns potentially requiring smaller investments. This makes post-campaign evaluation of coverage increasingly relevant to correctly assess future outbreak risk. Elsevier Science 2017-03-13 /pmc/articles/PMC5341736/ /pubmed/28216186 http://dx.doi.org/10.1016/j.vaccine.2017.02.008 Text en © 2017 The Author(s) http://creativecommons.org/licenses/by/4.0/ This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).
spellingShingle Article
Prada, J.M.
Metcalf, C.J.E.
Takahashi, S.
Lessler, J.
Tatem, A.J.
Ferrari, M.
Demographics, epidemiology and the impact of vaccination campaigns in a measles-free world – Can elimination be maintained?
title Demographics, epidemiology and the impact of vaccination campaigns in a measles-free world – Can elimination be maintained?
title_full Demographics, epidemiology and the impact of vaccination campaigns in a measles-free world – Can elimination be maintained?
title_fullStr Demographics, epidemiology and the impact of vaccination campaigns in a measles-free world – Can elimination be maintained?
title_full_unstemmed Demographics, epidemiology and the impact of vaccination campaigns in a measles-free world – Can elimination be maintained?
title_short Demographics, epidemiology and the impact of vaccination campaigns in a measles-free world – Can elimination be maintained?
title_sort demographics, epidemiology and the impact of vaccination campaigns in a measles-free world – can elimination be maintained?
topic Article
url https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5341736/
https://www.ncbi.nlm.nih.gov/pubmed/28216186
http://dx.doi.org/10.1016/j.vaccine.2017.02.008
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