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

Demographics, epidemiology and the impact of vaccination campaigns in a measles-free world: can elimination be maintained?
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 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.

Epidemiology, Mathematical models, Measles, SIR, Vaccines
0264-410X
1488-1493
Prada, J. M.
bfed01db-e940-4f2d-ab33-741d260b4c96
Metcalf, C. J.E.
95774dba-f27e-4bc6-bb7e-68a24f7ea051
Takahashi, S.
9a65ca68-97d5-47d6-b8bc-a7f8f240997e
Lessler, J.
02600458-d8b9-4f9a-96bc-f1295fc0a624
Tatem, A. J.
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Ferrari, M.
75741a06-6006-436e-a725-3943397aef6a
Prada, J. M.
bfed01db-e940-4f2d-ab33-741d260b4c96
Metcalf, C. J.E.
95774dba-f27e-4bc6-bb7e-68a24f7ea051
Takahashi, S.
9a65ca68-97d5-47d6-b8bc-a7f8f240997e
Lessler, J.
02600458-d8b9-4f9a-96bc-f1295fc0a624
Tatem, A. J.
6c6de104-a5f9-46e0-bb93-a1a7c980513e
Ferrari, M.
75741a06-6006-436e-a725-3943397aef6a

Prada, J. M., Metcalf, C. J.E., Takahashi, S., Lessler, J., Tatem, A. J. and Ferrari, M. (2017) Demographics, epidemiology and the impact of vaccination campaigns in a measles-free world: can elimination be maintained? Vaccine, 35 (11), 1488-1493. (doi:10.1016/j.vaccine.2017.02.008).

Record type: Article

Abstract

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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More information

Published date: 13 March 2017
Keywords: Epidemiology, Mathematical models, Measles, SIR, Vaccines

Identifiers

Local EPrints ID: 456317
URI: http://eprints.soton.ac.uk/id/eprint/456317
ISSN: 0264-410X
PURE UUID: d29515c2-e79d-4c1f-97b0-8de0ab40ac43
ORCID for A. J. Tatem: ORCID iD orcid.org/0000-0002-7270-941X

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Date deposited: 27 Apr 2022 02:18
Last modified: 06 Jun 2024 01:50

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Contributors

Author: J. M. Prada
Author: C. J.E. Metcalf
Author: S. Takahashi
Author: J. Lessler
Author: A. J. Tatem ORCID iD
Author: M. Ferrari

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