Measles: What progress in a decade?

Increased global measles vaccination coverage, an overall reduction in cases and improved surveillance are some of the highlights from a new report summarizing progress in measles control from 2000-2010. The report, published in WHO’s Weekly Epidemiological Record and the CDC’s Mortality and Morbidity Weekly Report provides an authoritative analysis on how measles control efforts have improved, the recent challenges with outbreaks including in Europe, and the efforts needed to reach all children with measles vaccine and meet the target of reducing global measles mortality by 95% by 2015.

Dr. Robert Perry, an author of the report and member of World Health Organization’s immunization team, responded to questions about the report’s major findings:

1. Overall, routine first-dose measles vaccination coverage is increasing globally, and a second opportunity for measles vaccination is provided in all countries. Which regions have made the most progress in coverage, and which are lagging? Why?

All regions have increased coverage with the first dose of measles vaccine since 2000. The most progress has been in the African and South-East Asia Regions. Though the gains are impressive, these two regions plus the Eastern Mediterranean still have not reached the target of 90% measles vaccination coverage. The challenge is improving coverage in large countries with weak routine immunization systems, such as India, the Democratic Republic of the Congo, Nigeria, Uganda and Pakistan. Even for countries with national coverage higher than 90%, less than half have at least 80% coverage in all districts with some districts lagging behind. Since measles is highly contagious and good at finding pockets of unvaccinated people, any groups with low vaccination coverage can be hit with an outbreak.

2. How has surveillance improved over the decade and why is this so important?

The big advances in measles surveillance have been shifting from just reporting numbers of cases, without any individual details like age or where they live, to reporting cases individually together with some basic information like date of rash onset, age, sex, vaccination status and where they live. A second advance has been moving from using just clinical signs for diagnosing measles to using laboratory tests to confirm the disease. A third has been collecting samples for viral genotyping.

These advances allow us to know more about who is getting measles, where and when, and to use this knowledge for identifying gaps in the vaccination program that might not be apparent from the vaccination coverage data.

3. What are the major remaining surveillance gaps?

We need to ensure that all countries are reporting all cases individually with laboratory confirmation of the disease. We also need to ensure that all outbreaks are thoroughly investigated; often these investigations can reveal gaps in vaccination programs that are not visible through analyzing individual cases or vaccination coverage data.

4. While there was steady progress in decreasing measles cases from 2000-2008, reported measles cases increased in 2009-2010. What happened?

In 2009-2010, large measles outbreaks were reported in countries in the African, Eastern Mediterranean, European, and Western Pacific regions.

5. What age groups are getting measles in the countries with the highest incidence (just give a couple of examples) and why?

Where routine vaccination coverage is low, such as in Nigeria, outbreaks primarily affect children under 5 years of age. Where routine coverage is good for the first and second dose but not high enough (>90% for both doses), outbreaks not only include cases among children under 5 but also affect large numbers of older children, adolescents, and even adults. These better-performing countries have a “honeymoon” period of up to several years with very few cases of measles. However, when enough susceptible individuals have accumulated over several years among adolescents and adults who had missed routine vaccination and campaigns, the country can have a large outbreak affecting older age groups.

6. The European region has experienced major measles outbreaks since 2009 – why are countries like France experiencing these large outbreaks?

In the European region the outbreaks were mixed. Some involved children from underserved groups with low vaccination coverage, often with spread to the surrounding population. Others, such as the outbreak in France, involved adolescents and young adults who had missed vaccination as infants and measles disease as children.

7. What are the key lessons we can take from the coverage and surveillance data?

Surveillance data helps to identify gaps in population immunity, underserved populations and areas of program weakness. These data show the need to look at routine measles vaccination coverage sub-nationally and to focus on strengthening those areas not reaching 80%. For campaigns these data emphasize the need to reach at least 90% of children not just nationally but also sub-nationally. The data also suggest some potential refinements to the campaign strategy, particularly the age range and the time between campaigns.

8. Which regions are on track to meet the 2015 targets? What do they need to do to stay on track?

All regions are making progress to the 2015 targets, though the progress may need to be faster in Africa and South-East Asia. Those regions on track need to maintain coverage at high levels at national and sub-national levels, ensure all children get a second dose through routine or high-quality campaigns, and use surveillance data to pick up any gaps and then respond to them.

9. What are the key strategies and support required for the regions that are off-track?

For South-East Asia the key is reducing measles in India. India needs to conduct high-quality catch-up campaigns in the remaining districts while implementing a second dose of measles vaccine through routine in the higher-performing states. India also needs to extend case-based surveillance with laboratory confirmation throughout the country. For Africa the key is building strong routine immunization systems in large countries like Nigeria and the Democratic Republic of the Congo. Throughout the region countries will need to ensure that campaigns target the appropriate age groups, based on surveillance data, and that the campaigns reach high coverage nationally and sub-nationally.

The new GAVI funding for introducing rubella may provide valuable support not only for controlling a preventable cause of birth defects but also will give countries a chance to fill any gaps in measles immunity. (For more on GAVI funding, see: https://www.gavialliance.org/support/nvs/rubella/)

Leave a Reply

Your email address will not be published. Required fields are marked *