Progress Toward Measles Elimination — Western Pacific Region, 2013–2017

Immunization Activities

MCV1 and MCV2 coverage data are reported annually to WHO and the United Nations Children’s Fund (UNICEF) from 36 of the 37 WPR countries and areas.^§ WHO and UNICEF estimate vaccination coverage for 27 countries/areas in the region, using annual government-reported survey and administrative data; for the remaining areas and territories, reported coverage data from immunization program monitoring are used. Regional MCV1 and MCV2 coverage rates were maintained at ≥95% and >90%, respectively, during 2013–2016 (Table 1). In 2016, 18 (50%) of 36 countries achieved ≥95% MCV1 coverage, and 11 (31%) reported ≥95% coverage with both MCV1 and MCV2. As of 2017, only two (5%) WPR countries and areas (Solomon Islands and Vanuatu) had not yet introduced MCV2. During 2013–2017, 18 national SIAs^¶ were conducted (Table 2); in addition, Japan conducted annual SIAs targeting schoolchildren aged 13 years and 17 years. Reported vaccination coverage was ≥95% in seven (39%) of the nationwide SIAs.

Surveillance Activities

Case-based measles and rubella surveillance data are reported monthly to WHO from all WPR countries and areas; 21 countries and areas of the Pacific Islands report data as one epidemiologic block.** The WHO Global Measles and Rubella Laboratory Network supports surveillance by providing laboratory confirmation and genotyping of reported cases. Suspected measles cases are confirmed based on laboratory findings, an epidemiologic link, or clinical criteria.^†† Key indicators of surveillance performance include 1) the number of suspected measles cases discarded as nonmeasles (target: ≥2 per 100,000 population); 2) the proportion of second-level administrative units with two or more nonmeasles discarded cases per 100,000 population (target: ≥80%); 3) the percentage of suspected measles cases with adequate investigation that includes all essential data elements^§§ (target: ≥80%); 4) the percentage of suspected measles cases with adequate specimens collected within 28 days of rash onset (target: ≥80%, excludes epidemiologically linked cases); and 5) the percentage of specimens with laboratory results available within 7 days after receipt in the laboratory (target: ≥80%). During 2013–2017, the number of WPR countries and areas^¶¶ that met the target for suspected cases discarded as nonmeasles per 100,000 population at the national level decreased from 11 (65%) to nine (53%), but increased from one (6%) to two (12%) at the subnational level. From 2013 to 2017, the percentage of suspected cases with adequate investigations decreased from 92% to 89%; the percentage of suspected cases with adequate specimens collected for laboratory testing decreased from 90% to 89%; and the proportion of blood specimens received by the laboratory with results available within 7 days increased from 84% to 98% (Supplementary Table, https://stacks.cdc.gov/view/cdc/53519).

Measles Incidence and Genotypes

WPR experienced a resurgence of measles during 2013–2016 (Figure), after a record low incidence of 5.9 cases per million population in 2012. During the resurgence, incidence of seasonal endemic measles virus transmission in China increased, and large-scale nationwide outbreaks occurred in other countries with endemic measles (Malaysia and the Philippines). During 2013–2016, after importations from countries with endemic disease, measles outbreaks also occurred in countries that had been verified as having eliminated endemic measles virus transmission (Australia, Cambodia, Japan, and South Korea), including a large-scale outbreak in Mongolia. An increase in importations also led to outbreaks in several countries with endemic, low-incidence measles, including New Zealand, Papua New Guinea, Singapore, Solomon Islands, and Vietnam. Annual regional measles incidence per 1 million population increased from 19.2 in 2013 to 68.9 in 2014, and then decreased to 5.2 in 2017, a historic low (Table 1). The predominantly detected circulating measles virus genotypes were H1 in China, B3 in the Philippines, and both D8 and D9 in Malaysia and Vietnam.

Regional Verification of Measles Elimination

After the request of the Western Pacific Regional Committee (5) for WHO to establish a formal mechanism for verification of elimination through the Regional Verification Commission, verification guidelines were finalized in April 2013 and revised in 2016 to include verification of rubella elimination. As of the September 2017 Regional Verification Commission meeting, a total of eight (47%) WPR countries and areas (Australia, Brunei, Cambodia, Hong Kong [China], Japan, Macao [China], New Zealand, and South Korea) have been verified as having achieved elimination of measles (6). After a nationwide outbreak in Mongolia during 2015–2016 that lasted longer than 12 months, the Regional Verification Commission determined that endemic measles virus transmission had been reestablished in Mongolia (7).

Discussion

The 2013–2016 measles resurgence in WPR was attributed to three factors. First, increased measles virus transmission occurred in countries with endemic disease (e.g., China, Malaysia, and the Philippines). Second, large-scale outbreaks occurred after importation of measles into countries with endemic, low-incidence measles. Third, multiple measles importations into countries or areas that had achieved elimination occurred, particularly in Mongolia, where a large outbreak persisted for >12 months and endemic measles virus transmission was reestablished.

Measles incidence in WPR declined to a historic low of 5.2 in 2017 because of achievement of control of the outbreaks in Vietnam (2013–2014) and Mongolia (2015–2016), burnout of the outbreak in the Philippines (2013–2014), and China’s accelerated control of measles after the 2010–2011 outbreak. However, the resurgence during 2013–2016 revealed ongoing and emerging challenges that need to be addressed. These challenges include changing measles epidemiology, with increased measles incidence occurring among adolescents, young adults, and infants too young to be vaccinated as well as heterogeneity of measles epidemiology among subnational areas and specific groups at risk within countries with large populations. In addition, the resurgence revealed systems weaknesses: immunization programs were unable to achieve and maintain high population immunity through routine immunization service delivery, and some national laboratories had insufficient capacity to conduct timely serologic testing during outbreaks. The challenges identified also included inadequately developed and implemented policies and processes for preventing measles resurgence and morbidity after virus introduction to the population, including delayed outbreak investigation, insufficient outbreak response, and nosocomial measles virus transmission. Finally, the resurgence revealed a need for greater involvement of local governments, private sectors, societies, and communities.

To address these challenges and to accelerate measles elimination efforts in WPR, the WHO Regional Office for the Western Pacific prepared a new strategy and plan of action for measles and rubella elimination in the Western Pacific that was endorsed by the 68th meeting of the WHO Regional Committee for the Western Pacific in October 2017 (5). The document details 31 strategies with accompanying activities in the following eight areas: 1) overall planning; 2) immunization services; 3) epidemiologic surveillance; 4) laboratory support; 5) program review and risk assessment; 6) outbreak preparedness and response; 7) partnerships, advocacy, information, education and communication, and social mobilization; and 8) progress monitoring and verification of elimination. The new regional strategy is designed to address specific challenges facing WPR countries and to serve as a resource for development of national plans of action (and subnational plans for countries with large populations), tailored to country-specific opportunities for achieving and maintaining measles elimination.

Collective efforts among WPR countries are important for achieving regional measles elimination. Working together to follow the recommended strategies and actions in the Regional Strategy and Plan of Action for Measles and Rubella Elimination could help WPR countries in their efforts to strengthen immunization programs to achieve and sustain high population immunity, maintain high-quality surveillance for rapid case detection and confirmation, and ensure outbreak preparedness and prompt response to contain outbreaks.