Immunization

Before the measles vaccine was introduced in 1963, 30 million people globally contracted measles each year. About 2 million of them died, usually because they were both malnourished and sick. (World Health Organization, April 28, 2017). Thankfully, worldwide vaccination efforts now mean that no child need die of measles. Measles is highly infectious, so 95 percent of the population must be immunized in order for herd immunity to protect the entire community. The United States achieved that: A decade ago, measles incidence was close to zero. Experts thought it would soon be eliminated in all developed countries, so public health workers focused on the very poorest nations.

Estimated Measles Vaccine Coverage — Selected Nations

While the majority of the world's countries are 90 percent or greater, there are still concerns in many areas as the immunization rate must be 95 percent of the population in order to be effective. The lowest rates of immunization are found in countries in Africa and Central Asia, but these countries also border nations with 80 percent and 90 percent immunization rates.

Data from World Health Organization, May 29, 2019.

Vaccine Exemption and Herd Immunity — United States

By June 2019, more than 1,000 measles cases had been reported in 28 U.S. states, the most since 1992 (measles was declared eliminated in 2000) (Centers for Disease Control, June 17, 2019). To understand what went wrong, note that many states allow personal or religious exemptions to immunization requirements. As the U.S. map shows, several states are not at that safe 94 percent — leaving many vulnerable, not only to discomfort but also to complications, including pneumonia, encephalitis, and even death.

States with vaccine exemptions include Washington, Oregon, California, Idaho, Montana, Nevada, Utah, Arizona, North Dakota, Wisconsin, Michigan, Ohio, Georgia, Florida, Maine, New Hampshire, Vermont, Pennsylvania, Maryland, Alaska, and Hawaii. MMR vaccination rate is more than 94 percent in Washington, Oregon, Idaho, Minnesota, Nevada, Utah, Arizona, Colorado, Kansas, Minnesota, Michigan, Iowa, Arkansas, Indiana, Ohio, Kentucky, Alabama, Georgia, Florida, New Hampshire, Maryland, and Alaska. Other states labeled on the map are New Mexico, Texas, Oklahoma, Missouri, Illinois, Tennessee, Virginia, South Carolina, Massachusetts, Rhode Island, Cincinnati, New Jersey, Delaware, and Washington, D.C.

Data from Mellerson et al., 2018.