Dataset Information

Characterizing the impact of spatial clustering of susceptibility for measles elimination.

ABSTRACT: Measles elimination efforts are primarily focused on achieving and maintaining national vaccination coverage goals, based on estimates of the critical vaccination threshold (V_c): the proportion of the population that must be immune to prevent sustained epidemics. Traditionally, V_c estimates assume evenly mixing populations, an invalid assumption. If susceptible individuals preferentially contact one another, communities may remain vulnerable to epidemics even when vaccination coverage targets are met at the national level. Here we present a simple method to estimate V_c and the effective reproductive number, R, while accounting for spatial clustering of susceptibility. For measles, assuming R₀?=?15 and 95% population immunity, adjustment for high clustering of susceptibility increases R from 0.75 to 1.29, V_c from 93% to 96%, and outbreak probability after a single introduction from <1% to 23%. The impact of clustering remains minimal until vaccination coverage nears elimination levels. We illustrate our approach using Demographic and Health Survey data from Tanzania and show how non-vaccination clustering potentially contributed to continued endemic transmission of measles virus during the last two decades. Our approach demonstrates why high national vaccination coverage sometimes fails to achieve measles elimination, and that a shift from national to subnational focus is needed as countries approach elimination.

SUBMITTER: Truelove SA

PROVIDER: S-EPMC6348711 | biostudies-literature | 2019 Jan

REPOSITORIES: biostudies-literature

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Characterizing the impact of spatial clustering of susceptibility for measles elimination.

Truelove Shaun A SA Graham Matthew M Moss William J WJ Metcalf C Jessica E CJE Ferrari Matthew J MJ Lessler Justin J

Vaccine 20181219 5

Measles elimination efforts are primarily focused on achieving and maintaining national vaccination coverage goals, based on estimates of the critical vaccination threshold (V<sub>c</sub>): the proportion of the population that must be immune to prevent sustained epidemics. Traditionally, V<sub>c</sub> estimates assume evenly mixing populations, an invalid assumption. If susceptible individuals preferentially contact one another, communities may remain vulnerable to epidemics even when vaccinati ...[more]

PMID: 30579756

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Project description:IntroductionIn seven southern African countries (Botswana, Lesotho, Malawi, Namibia, South Africa, Swaziland and Zimbabwe), following implementation of a measles mortality reduction strategy starting in 1996, the number of annually reported measles cases decreased sharply to less than one per million population during 2006-2008. However, during 2009-2010, large outbreaks occurred in these countries. In 2011, a goal for measles elimination by 2020 was set in the World Health Organization (WHO) African Region (AFR). We reviewed the implementation of the measles control strategy and measles epidemiology during the resurgence in the seven southern African countries.MethodsEstimated coverage with routine measles vaccination, supplemental immunization activities (SIA), annually reported measles cases by country, and measles surveillance and laboratory data were analyzed using descriptive analysis.ResultsIn the seven countries, coverage with the routine first dose of measles-containing vaccine (MCV1) decreased from 80% to 65% during 1996-2004, then increased to 84% in 2011; during 1996-2011, 79,696,523 people were reached with measles vaccination during 45 SIAs. Annually reported measles cases decreased from 61,160 cases to 60 cases and measles incidence decreased to <1 case per million during 1996-2008. During 2009-2010, large outbreaks that included cases among older children and adults were reported in all seven countries, starting in South Africa and Namibia in mid-2009 and in the other five countries by early 2010. The measles virus genotype detected was predominantly genotype B3.ConclusionThe measles resurgence highlighted challenges to achieving measles elimination in AFR by 2020. To achieve this goal, high two-dose measles vaccine coverage by strengthening routine immunization systems and conducting timely SIAs targeting expanded age groups, potentially including young adults, and maintaining outbreak preparedness to rapidly respond to outbreaks will be needed.

Dataset Information

Characterizing the impact of spatial clustering of susceptibility for measles elimination.

Publications

Characterizing the impact of spatial clustering of susceptibility for measles elimination.

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