Earlier this year, the federal Centers for Disease Control and Prevention said the U.S. was facing the biggest measles outbreak in seven years. Now, it is happening, just years after it was declared nearly eradicated in 2000. Just 63 cases a year occurred in the United States, and they were acquired outside the country, until this year.

So far, there have been at least 131 measles cases this year, with four fifths coming from seven measles outbreaks. Measles is one of the most contagious diseases known to man, with an infection rate of up to 90-95 percent for unvaccinated people who live with persons that are infected, such as in a classroom.

Measles can be a severe illness that causes symptoms like rash, high fever, cough, runny nose and red, watery eyes. In rare cases, patients face more serious complications, including pneumonia, encephalitis and even seizure and death.

The federal officials have long been stressing the importance of immunizing children against measles, mumps or rubella, but many parents refuse to vaccinate their children for religious reasons or because they think the shots may cause autism or other health problems.

A federal report released in late April found that one in four children does not comply with official vaccination recommendations because of missed doses of vaccines or vaccine lapses. Unvaccinated persons are at risk of acquiring measles themselves and also transmitting the disease to others, including children who are too young to be vaccinated.

Before the measles vaccination program, about 3–4 million persons in the U.S. had been infected each year, of whom 400–500 died, 48,000 had been hospitalized, and another 1,000 had developed a chronic disability from measles encephalitis.