(CNN) - A measles outbreak in New York has been called the largest in the state's recent history, and it's occurring at a time when there have been spikes in measles cases globally.
Since the outbreak emerged in September, measles has been diagnosed in at least 112 people across Rockland and Orange counties and at least 55 in New York City, according to numbers provided by the New York state and city health departments on Tuesday.
"I would say this is the largest measles outbreak that New York state has had in recent history," said Dr. Howard Zucker, the state commissioner of health.
"If you go back many decades ago when we weren't vaccinating, of course there were probably more outbreaks, but in my memory, I don't know of a measles outbreak that was this significant," he said. "We have immunized 13,000 children since this outbreak has begun."
The outbreak, which emerged after some children were infected on a visit to Israel in September, has particularly affected Orthodox Jewish communities, according to the New York City Health Department.
In New York City alone as of Tuesday, "we have 55 cases confirmed in Brooklyn," said Dr. Jane Zucker, assistant commissioner for the Bureau of Immunization at the NYC Health Department. She is of no relation to Dr. Howard Zucker.
The largest outbreak in New York City had 58 cases in 2013, she said. Now, "I'm certainly hoping that there are no further cases and we won't exceed that 58, but we're still in the middle of the outbreak."
The outbreak continues while there has been a spike in cases both nationwide and worldwide.
'Many of our cases were travel-associated'
Nationally, 2018 saw the second-highest number of measles diagnoses in more than two decades, with 273 cases. In 2015, an outbreak linked to Disneyland had 147 cases. There were 508 cases reported nationally in 1996, and some previous years saw higher numbers, too.
In the decade before 1963, when a vaccine became available, nearly all children got measles by the time they were 15, according to the US Centers for Disease Control and Prevention. It is estimated that 3 million to 4 million people in the United States were infected every year.
Then, in 1978, the CDC set a goal to eliminate measles from the United States by 1982. Measles was declared eliminated -- defined by absence of continuous disease transmission for greater than 12 months -- from the United States in 2000.
Recently, there has been a rise in unvaccinated children. A CDC report released in October said that the proportion of children receiving no vaccine doses by 2 years old rose from 0.9% among those born in 2011 to 1.3% among those born in 2015.
In general, the CDC recommends that people get the measles, mumps and rubella vaccine, or MMR, to protect against those viruses. The typical recommendations are that children should get two doses of MMR vaccine, the first at 12 to 15 months of age and the second at 4 through 6 years.
Measles is a highly contagious disease that is transmitted by sneezing and coughing, as well as direct contact with an infected person, according to the CDC.
Symptoms include fever and rash, usually lasting several days. Infected people are contagious from four days before through four days after the rash appears. Young children and pregnant women are among those at highest risk for severe complications, which can lead to death.
For every 1,000 children who get measles, one or two will die from it, according to the CDC.
The CDC recommends that everyone, including infants 6 to 11 months old, should be vaccinated before international travel.
"Many of our cases were travel-associated," Dr. Jane Zucker said of New York City.
"So unvaccinated children had acquired their infection overseas. There are large outbreaks in many countries in Europe, as well as a very large outbreak in Israel, and so people need to be protected before they travel," she said.
When a large percentage of the population is vaccinated, "herd immunity" will protect against the spread of disease among the unvaccinated or partially vaccinated, including babies.
"The increase in measles cases in Orthodox Jewish communities of Brooklyn demonstrates the importance of getting children vaccinated on time to prevent measles and not put other children at risk," New York City Acting Health Commissioner Dr. Oxiris Barbot said in a statement in November.
"The Health Department continues to strongly recommend unvaccinated individuals to get vaccinated now, especially before traveling internationally. If your child develops a rash or fever, contact your physician immediately and keep them home from school or child care," Barbot said.
'Overwhelming and scary and unexpected'
Unvaccinated travelers can quickly share the illness when they arrive in the United States, especially if they are part of a community that has low vaccination rates, Dr. Natasha Burgert, a board-certified general pediatrician in Kansas City, Missouri, wrote in an email Tuesday.
"This is a common scenario with measles because the US had eradicated the illness in the past. Most index cases are brought in from other less-controlled areas," Burgert said.
"When I hear about outbreaks of vaccine-preventable illness, my heart breaks for the kids and families suffering from illness. Measles is life-threatening and can have long-term consequences," Burgert said. "I am pleased to hear that clinicians are working aggressively to prevent additional spread, but there is more work to be done. History tells us that as the number of infected individuals continues to climb, we will begin to see deaths from this disease."
To address the outbreak in New York, Dr. Howard Zucker said Tuesday that many outreach efforts to communities have been made to encourage getting vaccinated and minimizing the risk when any student is not vaccinated. In the state of New York, measles immunization is required of children enrolled in schools, day cares and pre-kindergarten.
"Measles is one of the most contagious viruses. It's so contagious that nine out of 10 people will catch measles if they're in the same room as someone who has measles," said Dr. Tanya Altmann, founder of Calabasas Pediatrics Wellness Center in California and an American Academy of Pediatrics spokeswoman, who recently authored the book "Baby and Toddler Basics."
"Diseases like measles can travel very quickly across the country. It just takes one person on an airplane to infect 90% of unvaccinated people on that airplane and fly to any other state around the country," she said. "The take-home message is to make sure your children are up-to-date on vaccines."
At the time the outbreak emerged in New York last fall, Altmann said, she was attending the American Academy of Pediatrics' national conference in Orlando.
There, "the pediatricians I was talking to from the New York area were saying how it was so overwhelming and scary and unexpected," she said.
"They were opening their offices up on the weekend to help vaccinate anyone who wasn't up to date on the measles vaccine," she said. "The MMR vaccine is very safe, and two doses are very effective. If you have questions about the vaccine, talk to your health care provider."
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