Some reports claim that measles is the most contagious of all infectious diseases. The measles virus spreads easily by direct contact. Usually, this happens when infected people exhale minute droplets containing the virus particles; these droplets come in contact with other people and cause infection. In addition, people who have had the disease sometimes have low levels of virus for many decades following. These viruses also can infect other people.
Scientists use gene-sequence data to determine origin and transmission patterns of the measles virus. If the virus is established and circulating among members of a population, it is said to be endemic or indigenous. Currently, the virus is endemic in many African, Asian, and European countries. The Western Hemisphere has no endemic measles virus, and the only outbreaks occur when visitors and foreign travelers carry the virus from other countries.
Although the measles virus has been eliminated from the Western Hemisphere, there are reservoirs of the measles virus in many countries around the world (for example, in Africa, Asia, and Europe). Because of widespread travel, it is impossible to isolate measles by country or hemisphere. As recent cases in the Western Hemisphere show, outbreaks can still occur despite the absence of any established virus in a population. (High levels of immunization prevented the virus from becoming re-established through an epidemic.) Until eradication efforts succeed globally, countries must maintain high rates of vaccination in order to protect their populations.
Fortunately, there is no reservoir of the measles virus in animals. Unlike some viruses, the measles virus is specific to humans and cannot survive or replicate in any other animal species. If the virus is eradicated in the human population, there are no animal reservoirs that could reintroduce the virus.
Measles has a severe effect on the nutritional status of a child: well-nourished children who are otherwise healthy lose weight when they have the measles, while malnourished children become seriously ill. Treatment for measles consists of bed rest, medicines to control fever, and calamine lotion or other salves to relieve itching. Mortality rates are low in most developed countries where children have relatively good nutrition; however, complications occur rarely that require hospitalization: pneumonia, appendicitis, and severe infections of the brain or respiratory systems. In many developing countries where conditions of poor nutrition, poor sanitation, and lack of adequate health care are common, measles mortality rates are considerably higher, especially among children.
Measles vaccine (also called the Measles Virus Vaccine Live) is an inactivated form of the measles virus. The measles vaccine came on the market in the United States in 1963. In the United States, children usually receive a combined measles, mumps, and rubella vaccine (MMR).
The measles vaccine causes the body to produce antibodies against the virus, providing lifelong protection from the active virus. To ensure immunization, a person usually receives two doses of the vaccine: One dose at roughly 1 year of age and a second dose between 4 and 6 years of age or between 11 and 12 years of age. One dose of vaccine is only 95 percent effective (95 percent of people develop antibodies and become immune, whereas 5 percent fail to develop antibodies). The second dose helps catch the small number of people who do not develop antibodies after the first dose.
More than a decade of studies have shown few or no serious side effects associated with the measles vaccine. Those with a presumed higher risk of side effects include people with a history of allergic reactions to previous measles vaccine, the antibiotic neomycin, or other substances such as gelatin; pregnant women; infants younger than 6-12 months; people taking certain medications or receiving X-rays or cancer therapies; and people with immune deficiencies or severe illness with fever.
One 1998 study suggested a link between the measles vaccine and chronic bowel disease and autism, a developmental disorder. Reviews of this study, however, failed to confirm a cause-effect relationship. Additional studies of 3 million vaccinated children also showed no increased risk between the measles vaccine and severe adverse affects. Several independent groups, including the World Health Organization (WHO), found no severe effects associated with the vaccine despite more than 10 years of research.
The measles vaccine sometimes causes a range of mild side effects including low-grade fever, skin rash, itching, hives, swelling, reddening of skin, and weakness. Rarely, the vaccine causes seizures, double vision, headaches, vomiting, joint pain, or pain in the digestive system.
The ultimate benefit of eradication is the prevention of an estimated 1 million deaths in children each year. Eradication also saves money in the long run, as the case of smallpox demonstrates. When smallpox was eradicated in 1977, countries discontinued vaccination and prevention efforts. This meant an enormous savings in medical costs: By 1985, the United States was recovering the money it had invested in global eradication every 26 days. As with smallpox, money spent on measles eradication would eventually be recouped from savings in vaccination programs and medical treatment for measles patients.
Despite recent successes, several challenges remain in the fight for global eradication of measles. The magnitude of vaccination programs is staggering: Every day in the United States, 11,000 children are born, each requiring 15-19 doses of different vaccines by the time they are 1 1 /2 years old. It is logistically impossible to ensure that 100 percent of these children are vaccinated. Instead, vaccination programs can only aim to eliminate the risk of a major epidemic; this goal can be achieved for measles with a 90 to 95 percent vaccination rate.
In developing countries, the eradication challenge is even greater because lack of funds results in minimal health care programs and inadequate surveillance. Because cost effectiveness is critical in these countries, vaccination programs must target the most needy populations. For example, in countries with a high incidence of measles and a low vaccination rate, school-age children are likely to have developed a natural immunity to the virus (due to previous contact with the virus). These countries should target vaccination programs at a narrow age range, focusing on young children (who are less likely to have had previous contact with the virus). In contrast, countries like the sparsely populated Sahel of West Africa have a lower incidence of measles, and therefore many potentially susceptible adults. In this case, vaccination programs should best target a wider age range.
As campaigns succeed in eliminating measles from one country after another, experts predict that patterns of outbreaks and risks will shift. For example, older children and adults will be more likely to be susceptible; infants born to vaccinated mothers will be protected by maternal antibodies for a shorter period of time; people might become complacent about having their children vaccinated; and the number of susceptible people might increase, approaching the threshold level for epidemics. These changing patterns might require changes in vaccination strategies.
Estimates of the cost of global measles eradication run as high as $4.5 billion by the year 2010, an amount that includes $1.7 billion for vaccines in developing countries. In 1998 alone, the Centers for Disease Control and Prevention (CDC) budgeted $8 million for international programs to eliminate measles.
The measles vaccine itself is relatively inexpensive. (For countries in the Pan American Health Organization, each dose costs just 10 cents.) Eradication, however, requires additional expense and effort. These include extensive surveillance systems, education and health campaigns, and systems to ensure quick response to contain outbreaks. These expenses weigh heavily on some developing countries, whose health care systems are already stretched to their limits.
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