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 (administrative coverage is calculated by dividing the vaccine doses administered by the estimated target population) and immunization coverage surveys reported annually by 194 countries. During 2000–2016, estimated MCV1 coverage increased globally from 72% to 85% (Table 1), although coverage has not increased since 2009. Considerable variability in regional coverage exists. Since 2012, MCV1 coverage has remained essentially unchanged in the African Region (AFR) (72%), the Region of the Americas (AMR) (92%), and the Eastern Mediterranean Region (EMR) (77%). In the European Region (EUR), MCV1 coverage has declined from 95% to 93% since 2012, with 51% of EUR member states reporting lower coverage since 2013. In the South-East Asia Region (SEAR), MCV1 coverage increased slightly since 2012, from 84% to 87%. The Western Pacific Region (WPR) is the only region that has achieved and sustained MCV1 coverage >95% (since 2008). Since 2000, the number of countries with MCV1 coverage of ≥90% increased globally from 85 (44%) in 2000 to 119 (61%) in 2015, and to 123 (63%) in 2016. However, among countries with ≥90% MCV1 coverage nationally, the percentage with ≥80% MCV1 coverage in all districts declined from 46% (52 of 112) in 2010 to 45% (49 of 110) in 2015 and 36% (44 of 123) in 2016. Among the estimated 20.8 million infants who did not receive MCV1 through routine immunization services in 2016, approximately 11 million (53%) were in six countries with large birth cohorts and suboptimal coverage: Nigeria (3.3 million), India (2.9 million), Pakistan (2.0 million), Indonesia (1.2 million), Ethiopia (0.9 million), and the Democratic Republic of the Congo (0.7 million).

During 2000–2016, the number of countries providing MCV2 nationally through routine services increased from 98 (51%) to 164 (85%), with four countries (Guatemala, Haiti, Papua New Guinea, and Timor-Leste) introducing MCV2 in 2016. Estimated global MCV2 coverage steadily increased from 15% in 2000 to 60% in 2015 and 64% in 2016 (Table 1). During 2016, approximately 119 million persons received supplementary doses of measles-containing vaccine (MCV) during 33 mass immunization campaigns, known as supplementary immunization activities (SIAs),^¶ implemented in 31 countries (Table 2). Based on doses administered, SIA coverage was ≥95% in 20 (61%) SIAs. Among the six countries that conducted post-SIA coverage surveys, estimated coverage was ≥95% in three, 90%–94% in two, and 84% in one.

Disease Incidence

Countries report the aggregate number of incident measles cases**^,†† to WHO and UNICEF annually through the Joint Reporting Form. In 2016, 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. Nonetheless, surveillance was weak in many countries; fewer than half of countries (64 of 134; 48%) achieved the sensitivity indicator target of two or more discarded measles and rubella^§§ cases per 100,000 population in 2016 compared with 2015 (80 of 135; 59%).

During 2000–2016, the number of measles cases reported annually worldwide decreased 85%, from 853,479 in 2000 to 214,812 in 2015 and then to 132,137 in 2016; measles incidence decreased 87%, from 145 to 19 cases per 1 million population (Table 1). Compared with 2015, 2016 incidence decreased from 29 to 19 cases per million, although three fewer countries (173 of 194; 89%) reported case data in 2016 than did in 2015 (176 of 194; 92%).^¶¶ The percentage of reporting countries with fewer than five measles cases per million population increased from 38% (64/169) in 2000 to 69% (119/173) in 2016. During 2000–2016, measles incidence of fewer than five cases per million was sustained in AMR (Table 1).

During 2015–2016, the number of reported measles cases declined globally and in all regions (AFR, 31%; AMR, 98%; EMR, 71%; EUR, 84%; SEAR, 44%, and WPR, 11%). In addition to aggregate reporting, countries report measles case-based data to WHO monthly. In some countries large discrepancies exist between the two reporting systems. During 2016, some countries either did not report or reported only a fraction of monthly reported measles cases through the Joint Reporting Form (e.g., India reported 70,798 measles cases through monthly reporting, but only 17,250 through the Joint Reporting Form).

Genotypes of viruses isolated from measles cases were reported by 60 (55%) of the 110 countries that reported at least one measles case in 2016. Among the 24 recognized measles virus genotypes, 11 were detected during 2005–2008, eight during 2009–2014, six in 2015, and five in 2016, excluding those from vaccine reactions and cases of subacute sclerosing panencephalitis, a fatal progressive neurologic disorder caused by persistent measles infection (4).*** In 2016, among 4,796 reported measles virus sequences,^††† 666 were genotype B3 (36 countries); 44 were D4 (four); 1,407 were D8 (43); 87 were D9 (four); and 2,592 were H1 (13).

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 2000–2016, enabling derivation of a new series of disease and mortality estimates (5). Based on the updated data, the estimated number of measles cases declined from 29,068,400 (95% confidence interval [CI] = 20,606,800–55,859,000) in 2000 to 6,976,800 (95% CI = 4,190,500–28,657,300) in 2016. During this period, the number of estimated measles deaths declined 84%, from 550,100 (95% CI = 374,000–896,500) in 2000 to 89,780 (95% CI = 45,700–269,600) in 2016 (Table 1). Compared with no measles vaccination, measles vaccination prevented an estimated 20.4 million deaths during 2000–2016 (Figure).

Regional Verification of Measles Elimination

In 2016, four WHO regions had functioning regional verification commissions. In September 2016, the AMR regional verification commission declared the region free of endemic measles (6). In 2016, the EUR commission verified measles elimination in 24 countries (7). Two SEAR countries (Bhutan and Maldives) were verified as having eliminated measles in 2017 (8). The WPR commission reclassified Mongolia as having reestablished endemic measles virus transmission because of an outbreak that lasted >12 months; thus, five WPR countries (Australia, Brunei, Cambodia, Japan, and South Korea) and two areas (Macao Special Autonomous Region [SAR] [China] and Hong Kong SAR [China]) had verified measles elimination status in 2016 (9).

Discussion

During 2000–2016, increased coverage with MCV administered through routine immunization programs worldwide, combined with SIAs, contributed to an 87% decrease in reported measles incidence and an 84% reduction in estimated measles mortality. Measles vaccination prevented an estimated 20.4 million deaths during this period, and during 2016, for the first time ever, estimated measles deaths declined to fewer than 100,000. Furthermore, the number of countries with measles incidence of fewer than five per million population has increased, although considerable underreporting occurred, and AMR has maintained an incidence of fewer than five cases per million population during 2000–2016. The decreasing number of circulating measles virus genotypes suggests interruption of some chains of transmission. However, the 2015 global control milestones were not met, global MCV1 coverage has stagnated, global MCV2 coverage has reached only 64%, and SIA quality was inadequate to achieve ≥95% coverage in several countries. With suboptimal MCV coverage, outbreaks continued to occur among unvaccinated persons, including school-aged children and young adults.

The 2016 Mid-term Review of the Global Measles and Rubella Strategic Plan 2012–2020 concluded that measles elimination strategies were sound, and the WHO Strategic Advisory Group of Experts on Immunization endorsed its findings. The review noted, however, that implementation of the strategies needs improvement. Measures should focus on strengthening immunization and surveillance systems. The Measles and Rubella Initiative should increase its emphasis on using surveillance data to drive programmatic actions.

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, large differences between the estimated and reported incidence indicate variable surveillance sensitivity, making comparisons between countries and regions difficult to interpret. Finally, the accuracy of the results from the measles mortality model is affected by biases in all model inputs, including country-specific measles vaccination coverage and measles case-based surveillance data.

The decrease in measles mortality to fewer than 100,000 deaths in 2016 is one of five main contributors (along with decreases in mortality from diarrhea, malaria, pneumonia, and neonatal intrapartum deaths) to the decline in overall child mortality worldwide and progress toward the fourth United Nations Millennium Development Goal, but continued work is needed to help achieve measles elimination goals (10). Of concern is the possibility that the gains made and future progress in measles elimination could be reversed when polio-funded resources supporting routine immunization services, measles SIAs, and measles surveillance diminish and disappear after polio eradication. Countries with the highest measles mortality rely most heavily on polio-funded resources and are at highest risk for reversal of progress after polio eradication is achieved. Improved implementation of elimination strategies by countries and their partners is needed, with focus on increasing vaccination coverage with substantial and sustained additional investments in health systems, strengthening surveillance systems, using surveillance data to drive programmatic actions, securing political commitment, and raising the visibility of measles elimination goals.