Progress in Measles Control & Elimination
Progress in the Americas
The USA established its first measles elimination goal in 1966. Measles elimination appeared close in 1983, but subsequently outbreaks occurred among highly vaccinated school-age populations, leading to expensive outbreak control activities. In 1989, a two-dose measles vaccination strategy was recommended. From 1989–1991 there was a large measles resurgence in the USA (rubella and CRS also increased at that time). Almost one half of all measles cases and 90% of deaths occurred in unvaccinated preschool children. Control required immense efforts to deliver the first dose on time, demonstrating the critical importance of achieving and sustaining high and timely routine coverage.
The goal of eliminating measles from the Americas was set in 1994, the year when the region was declared polio-free. In Latin America and the Caribbean, routine services aimed to 'keep-up' high population immunity by vaccinating over 90% of each birth cohort and increasing the age for first dose to 12 months. In the early 1990's 'catch-up' campaigns, usually targeting children aged 9 months to 15 years were conducted, aiming to immunize all susceptible children who had accumulated over the previous years of routine vaccination. After approximately 4 years, 'follow-up' campaigns were done among children aged 1–4 years, to sustain high population immunity. Both types of campaigns included community-based 'mop-up' activities in areas where monitoring showed that campaign coverage was below 95%. Finally, once the goal of rubella elimination was added in 2003, 'speed up' campaigns were done among adults (of both sexes in all but three countries) up to age 40 years, to quickly reduce transmission. Although rubella was the primary motivator for the speed-up campaigns, all countries used combined MR or MMR vaccines. The age range for rubella vaccination campaigns was wider than that for measles as the lower R0 of rubella meant that a larger number of adults had been susceptible to rubella than for measles. Programmes were guided by close monitoring of progress including routine coverage, campaign coverage, case-based disease surveillance and virus surveillance. The last endemic case of measles was documented in November 2002, and that of rubella in 2009.
Progress in Other Regions
The success of measles elimination in the Americas encouraged the adoption of measles elimination goals in the eastern Mediterranean (EMR, 1997), European (EUR, 1998), western Pacific (WPR, 2005) and African (AFR, 2011) regions, with varying target dates for elimination. The south east Asia region (SEAR) retains a measles mortality reduction goal, but elimination is under discussion.
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Figure 1.
Reported measles incidence rates per million population by WHO region per year, 1980–2011.
AFR: African; AMR: Americas; EMR: Eastern Mediterranean; EUR: European; SEAR: South east Asia region; WPR: Western Pacific.
In AFR, measles transmission may have been interrupted briefly in southern Africa and Uganda, but since 2009 outbreaks have occurred across the region. Large outbreaks were reported in the Democratic Republic of Congo (DRC: 133,802 cases, 2011), Malawi (118,712 cases, 2010), Burkina Faso (57,489 cases, 2009), Zambia (28,989 cases, 2010–2011) and Nigeria (18,843 cases, 2011). Of these, Malawi, Burkina Faso and Zambia reported both high routine coverage and regular measles vaccination campaigns. Vaccination and long lulls between outbreaks increase the average age of infections. Between 2002 and 2009, the median age for a reported measles case was 36 months in countries with MCV1 coverage of less than 50%, vs 49 months in those with MCV1 coverage of 75% or greater. In Burkina Faso, Malawi and Zambia there were large numbers of cases among teenagers and adults, and the majority of cases in Malawi's 2010 outbreak were over 5 years of age.
Nine countries in EMR reported measles incidence of <one case per million persons in the presence of a sensitive and well-functioning nationwide surveillance system in 2011. In 2011, however, a major resurgence of measles occurred in conflict-affected and poorer countries with 35,923 cases reported to WHO-more than in 1997. Of these, almost half were from Somalia, and between 2600–5600 from each of Afghanistan, Pakistan, the Sudan and Yemen. In Somalia, low MCV coverage in areas where immunization services could not be provided for nearly 2 years led to a massive measles outbreak, primarily among children aged <5 years. Population movements led to measles virus transmission among refugees, and outbreaks in Ethiopia and Kenya.
In Europe, Finland implemented a two dose schedule early in the programme and is the only country to have sustained measles elimination. Catch-up campaigns, some going up to age 40 years, were implemented mainly in central and eastern Europe (CEE) and the newly independent states (NIS). From 2004–2006 outbreaks in CEE and NIS involved a high proportion of older and previously vaccinated persons whereas most transmission since then has been in unvaccinated persons. From 2009–2011, large outbreaks occurred in western Europe, as well as Bulgaria and Ukraine, and outbreaks continue to occur in several countries at the time of writing. These often began among groups having low coverage such as Roma and Sinti communities, Irish Traveller communities, anthroposophic groups and ultra-orthodox Jewish communities and spread to the wider population and to other countries. The majority of cases were among the unimmunized population, in infants younger than one year, adolescents and young adults. Low vaccine effectiveness, possibly related to cold chain failures and/or use of a more thermo-labile vaccine, was reported in Ukraine and nosocomial transmission contributed in France and elsewhere.
SEAR has implemented accelerated measles control strategies. India was the last country to offer a second opportunity for measles vaccination. A routine second dose has now been implemented in states with reported MCV1 coverage ≥80%. In states with reported MCV1 coverage <80%, catch-up campaigns reportedly reached almost 40 million children aged 9 months to 10 years (86–89% of target) in 2010–2011, with the final phase of the campaigns scheduled for completion by April 2013. The two other large countries in the region, Bangladesh and Indonesia, have much higher routine coverage but gaps remain, particularly in Indonesia.
WPR reported by late 2012 that the region was approaching interruption of endemic measles transmission. China has had 99% MCV1 WHO-UNICEF estimates of coverage (WUENIC) since 2010. It conducted subnational campaigns from 2003–2009 and a massive national catch-up campaign in 2010, reporting 95% coverage. China reported just under 10,000 cases to WHO in 2011 compared to 38000–131,000 cases per year in the previous decade and over a million cases in 1980 and 1981. Malaysia has relied chiefly on high routine coverage to control measles but regional heterogeneity in coverage, and delays in delivery of the second dose until age 7 years resulted in an outbreak in 2011 (Figure 2F) chiefly affecting <7 year olds. As elsewhere, an increased proportion of cases in WPR now occur among young infants and adults. A 2008–2009 outbreak in Vietnam started among unvaccinated university students. Vietnam conducted a campaign targeting 7–20 year olds in key provinces in 2008, and another in 2010 targeting 1–5-year-olds, and case numbers remain very low in 2012. Laos also implemented wide age range campaigns targeted at 9 month to 19 year olds in 2011. Measles genotyping indicates considerable measles introductions both between countries in the region, but also from outside.
The occurrence of outbreaks in countries after years of low incidence is due to the accumulation of susceptible persons. This is attributed to various challenges facing vaccination programmes, as illustrated below.