The goal of eradication efforts is to stop the global spread of the measles virus and thereby end the need for vaccination. Eradication is possible because there is a highly effective vaccine and the measles virus survives or replicates only in humans. This means that there is no hidden reservoir of the virus in animals that could lead to outbreaks in humans in the future.
To achieve global eradication, all countries must first eliminate any measles viruses that are established or circulating within the population. These elimination campaigns require ongoing surveillance and vaccination to prevent outbreaks from measles viruses imported from other countries.
In 1996, the World Health Organization (WHO) confirmed that global eradication of measles is feasible between 2005 and 2010 using current vaccines. To accomplish eradication, they urge that all countries (1) use a two-dose strategy for immunization; (2) include rigorous diagnosis and surveillance; (3) view measles outbreaks as an opportunity to raise awareness and political support for eradication; and (4) work closely with other countries. Moreover, the WHO urges developing countries to link their measles and polio vaccination efforts to prevent conflicts over limited resources.
Because of limited resources and logistical problems with delivering the vaccine, measles remains a serious problem in some developing countries. Experts warn that vaccine shortages may prevent these countries from effectively controlling outbreaks. They also warn that measles vaccination programs compete with polio eradication efforts in some countries, making it difficult to make progress against either disease.
Some experts believe that the United States has become complacent in its attitude toward measles. They say that the United States views measles as a mild disease and focuses on the safety and effectiveness of vaccinations rather than on maintaining vaccination coverage so that global eradication can be achieved. These experts believe that by delaying eradication efforts, many of the hard-won gains of the past decade will be wiped out.
In 1994, countries in the Western Hemisphere set a goal of eliminating measles by the year 2000. From 1987 to 1994, numerous countries supplemented their routine vaccination programs with catch-up campaigns. All these countries now have laboratories that can report data to a regional surveillance network. As a result, in 1996 over half of the countries exceeded 90 percent vaccination coverage. That year saw a total of 2,109 cases of measles, a record low. This represents only 0.3 percent of the global total of measles cases. In addition, more than 60 percent of the countries in the Western Hemisphere reported no cases of measles.
Support for global measles eradication began to form in 1989, when the World Health Assembly set a goal for 1995 of decreasing measles deaths by 95 percent compared with measles deaths during the prevaccination period. In 1990, the World Summit for Children resolved to vaccinate 90 percent of children by the year 2000. Countries in the Western Hemisphere, Europe, and the Eastern Mediterranean formed organizations to pursue regional goals.
Current data suggest that vaccination programs have eliminated the measles virus from much of the Western Hemisphere, the United Kingdom, and the West Bank and Gaza. Countries in Europe, the South Pacific, the Middle East, and Southeast Asia have increasingly used catch-up vaccination programs to supplement their routine vaccinations. These campaigns reached an additional 32.8 million children. As of 1998, catch-up programs are continuing in Australia, the Philippines, Romania, and Tunisia.
Surveillance is a critical component of measles eradication. Measles surveillance requires local, regional, and national efforts. Locally, doctors must work with microbiology labs to diagnose measles cases correctly. Regional and national laboratories then gather and analyze these data to determine the original source of the virus, how many other people might have come in contact with it, and how it might best be contained. Surveillance networks also monitor vaccination rates to determine the locations of populations especially at risk for measles epidemics. Without these data, measles elimination would not be possible, as countries could not see how best to use scarce resources of money and technology. Although most developed nations have adequate surveillance networks, many developing countries have only one national laboratory dedicated to the problem of measles elimination.
In the United States, populations at risk for reduced levels of vaccination include people of low income, minority groups, large families, and young mothers. People at risk for contracting measles include those living in the inner city or an area of a previous measles outbreak, women of childbearing age, college students, foreign travelers, and health care workers.
People who receive only one dose of vaccine are also at higher risk for contracting measles. In 1999, an outbreak in Anchorage, Alaska, started when a 4-year-old child, visiting from Japan, developed a measles rash. A month later, students at a local high school started coming down with the disease. A total of 33 cases was reported, with no deaths. Despite a high immunization rate at the school, the outbreak occurred because half of the students had only had one dose of the vaccine. One dose is only 95 percent effective. This left a window of opportunity for the virus. Of the 33 cases, 29 were students who had received at least one dose of vaccine. Afterward, school and health officials accelerated second-dose vaccinations in order to prevent future outbreaks.
Costs of measles vaccination programs vary depending on the strategy and goals of the program. In 1998, the Australian government budgeted $30 million for a vaccination program to immunize 95 percent of its children. The actual price for the measles vaccine varies. In the Americas, the vaccine is available at a cost of 10 cents per dose or 49 cents per dose if combined with the vaccines for mumps and rubella (German measles)—the MMR vaccine.
Cost estimates also must acknowledge that vaccination programs can lead to a decrease in medical costs for treating measles patients. According to one estimate, every $1 spent on measles vaccine saves $10.30 in medical costs and $3.20 in indirect or social costs.
In addition to routine vaccinations, there are three different types of vaccination programs, each with a different strategy and goal. Catch-up programs are one-time campaigns that aim to vaccinate all children 9 months to 14 years old, whether or not they have had measles or previous vaccinations. Keep-up programs are routine services that focus on vaccinating at least 90 percent of children at age 12 months in the years following the catch-up program. Follow-up programs take place at least once every four years and aim to vaccinate all children ages 1-4.
Public fears about possible adverse effects of the measles vaccine decrease vaccination rates. A study showed that in Wales, United Kingdom, vaccination rates fell roughly 14 percent (from 83 percent to 69 percent) after adverse publicity about the measles vaccine raised concern that the vaccine might cause chronic bowel disease or autism. However, intense scientific scrutiny has not confirmed any link. Experts warn that if such a decline in vaccination rates continues, it could undo recent progress that has almost eliminated measles in the United Kingdom.
Some researchers note that as the threat of measles declines, parents' concerns over safety take on greater importance. In Australia, of 1.1 million students offered immunization, only 86 percent received parental consent. In Chicago, the same populations that had suffered the highest incidence in a previous measles epidemic remained undervaccinated five years later. Even a free, mobile vaccination program had not increased vaccination rates to acceptable levels: More than 45,000 children in Chicago were still vulnerable to measles. Community outreach and education programs might improve this situation.
To prevent measles outbreaks, scientists estimate 95 percent of the population must be immune. In the United States, vaccination rates are at record levels: Coverage exceeded 90 percent for children roughly 1 1/2-3 years old and 95 percent for children ages 5-6 years. However, pockets of low immunization persist. In Chicago in 1994, coverage for children was 47 percent overall but only 29 percent for inner-city, African-American children. This occurred despite access to free vaccines and a measles outbreak in Chicago in 1989 that heightened awareness. Another study of young children in rural New York found that only 85 percent were vaccinated. And, according to the Centers for Disease Control and Prevention (CDC), just over one-half of all schoolchildren in the United States have had both doses of the vaccine. Note that one dose is only 95 percent effective. (Ninety-five percent of people with one dose will gain immunity; the other 5 percent will fail to develop antibodies and will be unprotected.) Even when both doses are given, some people fail to form antibodies, although the probability of this happening is extremely low.
In 1997, there was a resurgence of measles epidemics across the Americas, mainly in Brazil and Canada. In these countries, vaccination rates had fallen among some populations, making them more susceptible to epidemics. Gene-sequence data indicate that most of these outbreaks resulted from strains of measles virus imported from Europe and Asia that subsequently spread among unvaccinated or undervaccinated populations. This suggests that despite the absence of established measles virus, populations can still be at risk for epidemics.
Eradication is only feasible if all countries eliminate all of the measles virus. Elimination requires that at least 90 percent and possibly as much as 95 percent of a population have immunity. At this time, all countries in the Western Hemisphere have achieved this goal, with vaccination rates over 90 percent. Worldwide, however, vaccination rates are only 82 percent. Rates are highest (93 percent) in the Americas and the Western Pacific. Rates are lowest (57 percent) in Africa; 10 African countries have rates of less than 50 percent. Moreover, 57 percent of the world's children live in areas with vaccination rates below 50 percent. More than two-thirds live in Africa or Southeast Asia.
In 1997, several vaccination campaigns targeted at-risk populations in an attempt to raise overall vaccination rates. These campaigns included five countries in Africa, four in Southeast Asia, and one in the South Pacific region. As a result, more than 5.8 million children were vaccinated.
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