— -- Medical experts considered measles essentially eradicated in this country thanks to large scale vaccination. But with at least 64 confirmed cases of measles this month, the disease seems on pace to have its worst year in nearly two decades.
Many young doctors are slow to recognize measles and may not realize its potential dangers, said Dr. Richard Besser, ABC News' chief health and medical editor. This may have contributed to the current outbreaks at Disneyland in California and in 11 other states and Mexico, he said.
“Pediatricians who have never seen the measles tend to undervalue the vaccination and it’s concerning they may miss a child with measles,” Besser said, adding that he, himself, hasn’t seen a case in more than 20 years.
Earlier this week, an infectious disease specialist at Children's Hospital of Philadelphia echoed that thought in an essay in the journal Annals of Internal Medicine. In the opinion piece, Dr. Julia Shaklee Sammons implored doctors to become more familiar with measles symptoms now that infections from the virus are on the rise.
“It is essential that providers maintain a high level of suspicion for measles ... and are able to recognize its clinical features,” she wrote.
People infected with measles are highly contagious for at least four days before symptoms including fever, pink eye and a telltale rash appear. Unfortunately, these are also symptoms of many other common diseases, Besser said, which is why it’s so hard to diagnose -- and why it’s essential to recognize it early.
Parents who delay or refuse vaccinations for their children may also contribute to the rise of measles infections, Besser said.
Many counties in California, for example, are below the 92 percent vaccination rate required for “herd immunity” the threshold of vaccinated individuals needed to protect even those who don’t receive the vaccination, according to state health officials. The opt-out rate for vaccinations has doubled in the past seven years.
"There's discredited science linking vaccines to autism. As a parent and pediatrician, there's no concern with the vaccine. What happens is that when a vaccine works really well, like the measles vaccine, people think they don't need it and then it comes back and we see these kinds of cycles," he said.
Besser noted that one year before the introduction of the measles vaccine in 1962, there were 481,530 reported cases nationwide. In 2004, there were 37 cases, according to the U.S. Centers for Disease Control and Prevention. That number has been creeping up steadily each year.
The CDC recommends all children get two doses of MMR (Measles, Mumps, Rubella) vaccine, starting with the first dose at 12 through 15 months of age, and the second dose at 4 through 6 years of age. The agency and most other medical organizations state that the vaccination has led to a 99 percent reduction in cases of the measles in the U.S.
Measles can be a deadly disease, Besser stressed.
“Before we began vaccinating, 500 people died a year from measles and it’s still one of the biggest global killers of children.” Besser said.
Dr. Besser is answering your questions about measles all morning on Twitter. And follow ABC News Health on Twitter for the latest health and medical news.