Vaccination strategies for measles control and elimination: time to strengthen local initiatives

Abstract

Background: Through a combination of strong routine immunization (RI), strategic supplemental immunization activities (SIA) and robust surveillance, numerous countries have been able to approach or achieve measles elimination. The fragility of these achievements has been shown, however, by the resurgence of measles since 2016. We describe trends in routine measles vaccine coverage at national and district level, SIA performance and demographic changes in the three regions with the highest measles burden.

Findings: WHO-UNICEF estimates of immunization coverage show that global coverage of the first dose of measles vaccine has stabilized at 85% from 2015 to 19. In 2000, 17 countries in the WHO African and Eastern Mediterranean regions had measles vaccine coverage below 50%, and although all increased coverage by 2019, at a median of 60%, it remained far below levels needed for elimination. Geospatial estimates show many low coverage districts across Africa and much of the Eastern Mediterranean and southeast Asian regions. A large proportion of children unvaccinated for MCV live in conflict-affected areas with remote rural areas and some urban areas also at risk. Countries with low RI coverage use SIAs frequently, yet the ideal timing and target age range for SIAs vary within countries, and the impact of SIAs has often been mitigated by delays or disruptions. SIAs have not been sufficient to achieve or sustain measles elimination in the countries with weakest routine systems. Demographic changes also affect measles transmission, and their variation between and within countries should be incorporated into strategic planning.

Conclusions: Rebuilding services after the COVID-19 pandemic provides a need and an opportunity to increase community engagement in planning and monitoring services. A broader suite of interventions is needed beyond SIAs. Improved methods for tracking coverage at the individual and community level are needed together with enhanced surveillance. Decision-making needs to be decentralized to develop locally-driven, sustainable strategies for measles control and elimination.

Keywords: Campaigns; Elimination; Measles; Routine immunization.

Fig. 1

Areas of low MCV1 coverage in both 2000 and 2019 in AFR, EMR and SEAR. MCV1 coverage at the second administrative level (district or equivalent units) was estimated by Sbarra et al. [12] using survey data and geostatistical models. Areas classified as ‘barren or sparsely vegetated’ based on European Space Agency Climate Change Initiative (ESA-CCI) satellite data [15] or with fewer people than 10 per 1 × 1-km pixel based on WorldPop estimates [16] are masked in dark grey. Countries not included in the Sbarra et al. analysis are masked in light grey

Fig. 2

Plots showing the estimated breakdown of under-1-year-olds not receiving MCV by characteristic per country for countries with a full set of data, in AFR, EMR and SEAR. Panel a (left) shows countries with MCV1 coverage ≤ 80% and panel b (right) shows countries with MCV1 coverage > 80% according to WUENIC 2018. Estimated numbers of unvaccinated children were calculated from geospatial estimates of MCV1 coverage using methods described in Sbarra et al. [12] and population estimates from WorldPop [16], using the geographic distribution of < 1-year-old children in each country as a proxy for the geographic distribution of children of the target age for MCV1 vaccination. Conflict areas were identified using data from the ACLED [17] and Uppsala [18] conflict data programmes, 2018. The programmes provide geolocated data on conflict events, and here (following Wagner et al. [19]), conflicts resulting in fatalities in the 2 years prior to the period of study were aggregated and a buffer of 50 km was applied to the conflict fatalities data to identify ‘conflict-affected’ areas. Remote areas were defined as those with travel time > 3 h to the nearest settlement of > 50,000 people using estimates from Weiss et al. [20] and the distribution and extent of urban areas were identified using estimates from the Global Human Settlement framework [21]