The Lancet Infectious Disease
Jul 2011 Volume 11 Number 7 Pages 489 – 578
Measles once again
The Lancet Infectious Diseases
An effective vaccine against measles has been available for the past 40 years. Before its introduction in 1963 there were almost 135 million cases of measles and over 6 million measles-related deaths per year. Globally, thanks to this vaccine the number of measles deaths worldwide fell by 78% between 2000 and 2008, from an estimated 733 000 to 164 000.
However, despite these efforts, it is hard to believe that in the 21st century measles remains a leading vaccine-preventable cause of deaths in children younger than 5 years old. The disease is still endemic in many parts of Europe. In the past 2 years, Austria, France, Germany, Ireland, Italy, the Netherlands, Spain, and the UK have all seen outbreaks. In 2010, more than 27 795 cases of measles were reported in Europe, and 21 853 were reported during the 2009—10 outbreak in Bulgaria where 25 people died.
In USA during the 1980s, the number of measles cases was low but a big increase occurred in 1989 with almost 18 000 cases reported. Lack of a second dose of measles, mumps, and rubella (MMR) vaccine could have decreased the level of immunity among the school-age population, among whom most of the cases were reported. Subsequently, two rounds of vaccination were recommended. At the end of 2000, thanks to vaccination, the ongoing transmission of endemic measles was declared eliminated in the USA. However, this year from January 1 to May 20, 118 cases were reported in the USA. 46% of the cases were imported, most from countries in the WHO European region.
Before the era of vaccination, immunity against measles was acquired by natural infection or by protection given by antibodies transmitted from the mother to the fetus during gestation. Measles transmission requires contact between a susceptible person and the infectious secretions of a person with measles. The incidence of measles varies cyclically. Incidence rises as susceptible individuals enter the population. Acquisition of immunity through exposure to the virus or vaccination decreases the number of susceptible individual in the population and measles incidence falls. The interval between epidemic peaks is proportional to the number of susceptible individuals that accumulate over time. In the presence of vaccination, the interval between peaks of disease can be 10 years; without vaccination, the interval can be 3—4 years. A decline in the uptake of immunisation in the past decade has increased the susceptible population and measles has resurged.
Elimination of measles, defined as the interruption of indigenous transmission, is difficult because the disease is very contagious and transmissible before an infected person shows signs of illness. Ideally, two doses of MMR vaccine given to 95% of children are required to halt the spread of the virus. By 2009 only 60% of countries worldwide had achieved 90% coverage with at least one vaccine dose. Difficulty accessing services, religious beliefs, and vaccine scepticism are only part of the reasons for low coverage. Better organisation of the vaccination systems is required—for example, 10% of children receive one dose of vaccine but then miss the second shot. Lack of reminders and difficulty tracking moving families are among the weaknesses of the vaccine system.
However, elimination is not impossible. Measles was eliminated from the Americas in 2000, but progress towards elimination in the European region has faltered. By 2010, 30 of the 53 European countries had reached the target of a measles incidence of fewer than one case per million population. The WHO Europe strategic plan for measles 2010—15 sets targets of 90% measles vaccination coverage, and reductions in the number of cases to fewer than five per million and in mortality by 95% compared with 2000 levels.
Additional effort and resources from European states are needed to reach the above targets. Vaccine acceptability could be improved through better communication with the public. Thought needs to be given to targeted messaging campaigns and perhaps the recruitment of public figures as advocates for vaccination. Catch-up vaccination campaigns outside the routine system are needed to cover susceptible populations. Commitment from governments, donors, and parents is needed to make measles a disease of the past. Despite recent outbreaks, elimination in Europe in the in the next 4 years should be achievable, and would inspire efforts in developing regions, which still have the highest burden of the disease: global eradication of the disease in this generation would spare future generations from this preventable disease.