Progress Toward Regional Measles Elimination — Worldwide, 2000–2015

Immunization Activities

To estimate coverage with MCV1 and the second dose of measles-containing vaccine (MCV2) through routine immunization services,^§ WHO and the United Nations Children’s Fund (UNICEF) use data from administrative records and surveys reported annually by 194 countries. During 2000–2015, estimated MCV1 coverage increased globally from 72% to 85%, although coverage has not increased since 2009. The number of countries with ≥90% MCV1 coverage increased from 84 (44%) in 2000 to 129 (66%) in 2012, but then declined to 119 (61%) in 2015. Since 2003, countries also have reported the number of districts with ≥80% MCV1 coverage. Among countries with ≥90% MCV1 coverage nationally, the percentage with ≥80% MCV1 coverage reported in all districts increased from 2% of countries (one of 43) in 2003 to 44% (57 of 129) in 2012 and then declined to 39% (47 of 119) in 2015. Among the estimated 20.8 million infants who did not receive MCV1 through routine immunization services in 2015, approximately 11 million (53%) were in six countries: India (3.2 million), Nigeria (3 million), Pakistan (2 million), Indonesia (1.5 million), Ethiopia (0.7 million), and the Democratic Republic of the Congo (0.6 million).

During 2000–2015, the number of countries providing MCV2 nationally through routine immunization services increased from 97 (51%) to 160 (82%), with six countries (Angola, Malawi, Mozambique, Nepal, Sierra Leone, and Zimbabwe) introducing MCV2 in 2015. Estimated global MCV2 coverage increased from 15% in 2000 to 61% in 2015. During 2015, approximately 184 million persons received MCV during mass immunization campaigns known as supplementary immunization activities (SIAs)^¶ implemented in 41 countries, with 32 (78%) providing one or more additional child health interventions during the SIA (Table 1). Based on doses administered, SIA coverage was ≥95% in 21 (51%) countries; however, among the four countries conducting post-SIA coverage surveys, only one estimated coverage at ≥95%.

Disease Incidence

Countries report the number of measles cases**^,†† from either case-based^§§ or aggregate surveillance systems to WHO and UNICEF annually. In 2015, 189 (97%)^¶¶ countries conducted case-based surveillance in at least part of the country, and 191 (98%)*** had access to standardized quality-controlled testing through the WHO Global Measles and Rubella Laboratory Network. However, surveillance is weak in many countries, and 43% did not achieve the sensitivity indicator of reporting ≥2 discarded measles^††† cases per 100,000 population

During 2000–2015, the number of measles cases reported annually worldwide decreased 70%, from 853,479 to 254,928, and measles incidence decreased 75%, from 146 to 36 cases per 1 million population (Table 2). During 2013–2015, incidence declined from 40 to 36 per 1 million, although fewer countries reported case data in 2015 (169) than did in 2013 (176).^§§§ The percentage of reporting countries with an incidence of <5 cases per 1 million increased from 38% (64 of 169) in 2000 to 58% (98 of 168) in 2014, and to 65% (109 of 169) in 2015. During 2000–2015, the Region of the Americas (AMR) maintained measles incidence of <5 cases per 1 million.

From 2014 to 2015, the number of reported measles cases increased 33% in the African Region (AFR), 18% in the Eastern Mediterranean Region (EMR), and 83% in the European Region (EUR), primarily because of outbreaks in several countries. There was minimal change in reported cases in the South-East Asia Region (SEAR), and reported cases decreased 78% in AMR, with interruption of outbreaks in Brazil, Canada, and the United States. In the Western Pacific Region (WPR), reported measles cases declined 50%, with decreases in the three most populous countries in the region: China, the Philippines, and Vietnam (Table 2).

Genotypes of viruses isolated from measles cases were reported by 80 (51%) of the 157 countries that reported measles cases in 2015. Among the 24 recognized measles virus genotypes, 11 were detected during 2005–2008, eight during 2009–2014, and six during 2015, excluding those from vaccine reactions and cases of subacute sclerosing panencephalitis, a fatal progressive neurologic disorder caused by persistent measles infection^¶¶¶ (4). In 2015, among 8,076 reported measles virus sequences,**** 847 (from 48 countries) were genotype B3; 70 (10 countries) were D4; 1,801 (52 countries) were D8; 76 (10 countries) were D9; one was G3; and 5,281 (20 countries) were H1 (Table 1).

Disease and Mortality Estimates

A previously described model for estimating measles disease and mortality was updated with new measles vaccination coverage data, case data, and United Nations population estimates for all countries during 2000–2015, enabling a new series of disease and mortality estimates (5,6). According to the updated data, the estimated number of measles cases declined from 32,768,300 (95% confidence interval [CI] = 23,393,300–63,222,700) in 2000 to 9,719,600 (CI = 5,731,800–35,451,000) in 2015. During this period, the number of estimated annual measles deaths decreased 79%, from 651,600 to 134,200 (Table 2). Compared with no measles vaccination, measles vaccination prevented an estimated 20.3 million deaths during 2000–2015 (Figure).

Regional Verification of Measles Elimination

In September 2016, the AMR regional verification commission declared the region free of endemic measles (7). The WPR regional verification commission reclassified Mongolia as having reestablished endemic measles virus transmission because of an outbreak that lasted for >1 year; thus, five WPR member states have been verified as having eliminated endemic measles (8). In 2015, the EUR regional verification commission verified measles elimination in 21 countries (9).

Discussion

During 2000–2015, increased coverage worldwide with routine doses of MCV, combined with SIAs, contributed to a 75% decrease in reported measles incidence and a 79% reduction in estimated measles mortality. During this period, measles vaccination prevented an estimated 20.3 million deaths. Moreover, the number of countries with measles incidence <5 per million has increased, although there is a large amount of underreporting. The decreasing number of circulating measles virus genotypes suggests interruption of some chains of transmission. However, despite progress since 2000, the 2015 global control milestones and regional measles elimination goals were not achieved and much effort is needed if elimination in five of six regions is to be achieved by 2020. Countries and immunization partners need to substantially increase their commitment for additional financial and human resources to 1) enable public education on the importance of vaccination; 2) strengthen health systems with staff, outreach services, and access to reliable vaccine supply to deliver 2 doses of measles vaccine; 3) improve surveillance; and 4) invest in research and innovations to overcome hurdles to achieving high vaccination coverage.

The 2015 global control milestones and regional measles elimination goals were not met because vaccination coverage gaps persist. Globally, MCV1 coverage has stagnated at 84%–85% since 2009 and MCV2 coverage only reached 61% in 2015. SIA quality was inadequate to achieve ≥95% coverage in the majority of countries. Furthermore, the discrepancy between high SIA coverage reported by administrative methods and lower coverage found by a limited number of post-SIA coverage surveys indicates that SIA quality might also be inadequate in countries with high reported administrative coverage. Countries need to allocate more time for early planning and preparation for high-quality immunization campaigns, with careful assessment of pre-SIA readiness, well-conducted intra-campaign and postcampaign monitoring, and proper implementation of appropriately budgeted activities to vaccinate persons missed during the SIA.

The findings in this report are subject to at least three limitations. First, SIA coverage data might be biased by inaccurate reports of the number of doses delivered, doses administered to children outside the target age group, and inaccurate estimates of the target population size. Second, there are large differences between the estimated and reported incidence, indicating variable surveillance sensitivity, making comparisons difficult; in addition, not all ill persons seek care. Finally, misclassification might occur for reported cases that are not laboratory-confirmed or in countries that report aggregate numbers of unconfirmed cases rather than case-based data for confirmed cases.

The decrease in measles mortality is one of four main contributors (the others are decrease in mortality from diarrhea, malaria, and pneumonia) to the decline in overall child mortality worldwide and progress toward Millennium Development Goal 4, but continued work is needed to help achieve regional elimination (10). Of serious concern is the possibility that the gains made so far and future progress in measles control and elimination could be threatened if polio-funded resources that support routine immunization services, measles SIAs, and measles surveillance activities diminish or disappear following polio eradication. Those countries with the highest measles mortality rely most heavily on polio-funded resources and are at highest risk if these resources are not transitioned to adequately support other parts of the immunization program after polio eradication is achieved. Countries and partners need to act urgently to secure political commitment, raise the visibility of measles, increase vaccination coverage, strengthen surveillance, and mitigate the threat of resources for immunization programs decreasing once polio eradication is achieved.