At least 127 people in 15 states have come down with the measles, the biggest outbreak in the United States in more than 10 years, Reuters reported.

Cases started springing up in May, when more than 70 people in a dozen states became ill. According to federal health officials, most of the victims were not vaccinated against the highly contagious virus.

In a statement, the Centers for Disease Control and Prevention said the outbreak has been traced to travelers who became sick overseas, returned to the United States and infected others.

The news comes on the heels of public health officials' stressing the importance of immunizing children.

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"What concerns me is the trend of more and more people not vaccinating their children because of fears that vaccines cause autism — although no studies have proven this to be true," Dr. Joseph Rahimian, an infectious disease specialist at St. Vincent's Hospital in Manhattan, told FOXNews.com in May.

Last month British health officials said measles had become an epidemic in that country for the first time since the mid-1990s due to parents not getting their children vaccinated.

"With the whole debate about vaccines — and now parents due to their personal beliefs not vaccinating their children — what we are seeing now is that we are going to have these epidemic outbreaks throughout the country," said Dr. Manny Alvarez, managing editor of health at FOXNews.com.

"If this continues, we will see outbreaks throughout the entire developed world — something we have never seen before," he added.

The MMR vaccine (measles, mumps, and rubella) is the safest protection you can give your child against this virus, according to the CDC.

The agency recommends that children should be given their first dose of the MMR vaccine around 12 to 15 months of age. The second dose is recommended before the start of kindergarten, between the ages of 4 to 6.

The National Institutes of Health also recommends all adults 18 years or older born after 1956 should receive an MMR vaccine if they are uncertain of their immunization status or if they have only had one shot prior to entering school.

Measles is caused by a virus that normally grows in cells that line the back of the throat and the lungs.

"This is a very contagious disease," Alvarez said. "It's very difficult to eradicate once you have it."

Typical symptoms include:

— Coughing

— Runny nose

— High Fever

— Rash (which usually starts on the face and spreads to the rest of the body)

FAST FACTS: The Measles and Outbreaks

Measles remains a leading cause of death among children in poor countries.

"What you have to remember is that 250,000 children die from this virus every year," Alvarez added. "So, vaccinations have to be a priority for parents because at the end of the day if you get measles, you can live through it, but in some particular cases you're going to have complications."

About one in five measles sufferers experiences more severe illness, which can include diarrhea, ear infections, pneumonia, encephalitis, chronic neurological deficits and even death.

States with cases now include Arizona, Arkansas, California, Georgia, Hawaii, Illinois, Louisiana, Michigan, Missouri, New York, New Mexico, Pennsylvania, Virginia, Wisconsin and Washington state, as well as Washington, D.C., according to the CDC.

This latest outbreak comes eight years after the virus was declared practically dead in the United States, thanks to a vaccination program that began in the 1960s.

Click here to read more on this story from Reuters.

Click here for more information on the outbreak from the CDC.