Return of the measles: a recent outbreak of the highly contagious but preventable disease has renewed the debate on vaccination.

• Author: Smith, Patricia

In 2000, American health officials declared that the measles, one of the nastiest and most contagious of all childhood diseases, had been eliminated from the United States. But the celebrations turned out to be premature.

The measles is back. Its telltale rash of red spots has shown up in more than 140 new cases as the disease has spread across the country since an outbreak began in December. Health officials blame the resurgence on a growing anti-vaccination movement based on the discredited belief that some vaccines, including the one for measles, are dangerous for children.

"We can expect to see many more cases of this preventable disease unless people take measures to prevent it," says Dr. Gilberto Chavez, the deputy director of the California Center for Infectious Diseases.

The outbreak started at Disneyland in Southern California when a visitor infected with the virus passed it on to seven other visitors, six of whom weren't vaccinated. From there, it's spread to 17 states and the District of Columbia.

Word that the disease is on the loose has created fear in the places where cases have popped up, especially among parents of young children: Some have kept babies out of daycare centers, worried they'll be exposed. People have flooded doctors' offices to get the vaccination. In Orange County, California, where the outbreak began, schools temporarily banned unvaccinated students from attending class.

The fear is justified: Measles spreads through the air (see box) and can cause severe complications. They include deafness, pneumonia, and encephalitis (a swelling of the brain that can be fatal or result in brain damage). Children under 5 are most likely to suffer complications; almost 1 in 3 cases in young children require hospitalization.

Before vaccines for measles became widespread in 1963, millions of Americans were infected annually, with 400 to 500 dying each year. Worldwide, there are still about 20 million cases annually, mostly in poorer countries in Asia and Africa; in 2013, about 146,000 people died of measles.

Anti-Vaccine Movement

The reason for the current outbreak in the U.S. is that more and more Americans are going unvaccinated. According to the World Health Organization, the measles vaccination rate in 2013 was 91 percent in the United States--lower than in Zimbabwe or Bangladesh. And vaccination rates are much lower in some American communities: In Orange County, for example, some schools report that 50 to 60 percent of...