NEW CITY, N.Y. – The number of measles cases in the United States so far this year has surpassed 2017 with the potential for about a quarter of the highly contagious respiratory infections to be occurring in one New York county north of New York City.

Nationwide as of Oct. 6, the most recent nationwide data available, 142 measles cases had been reported, according to the federal Centers for Disease Control and Prevention. The number of people sickened, mostly unvaccinated, exceeded the 2017 total of 120 in mid-August.

As of Friday, Rockland County had 46 confirmed cases and nine suspected cases, according to the county's health commissioner, Dr. Patricia Ruppert. A month ago, Rockland County Health Department officials were worried about an outbreak and offering emergency measles vaccination clinics because a traveler from Israel had visited an ultra-Orthodox Hasidic synagogue and a sukkah, a temporary structure built for the weeklong Jewish festival of Sukkot, near a Jewish boys school in New Square, New York.

"There's a component ... that are not in favor of vaccines," said Dr. Howard Zucker, New York state's health commissioner. "We need to dispel any worries that they have."

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None of those infected in Rockland County were fully vaccinated, Ruppert said. The state has banned unvaccinated students from attending classes in three communities if their school has a vaccination rate of 70 percent or lower.

Two doses of the measles, mumps and rubella vaccine, generally given at age 12 to 15 months with a booster at 4 to 6 years old, are 97 percent effective in preventing measles. One dose is 93 percent effective, according to the CDC.

The measles virus is transmitted via the misty droplets that come when an infected person coughs, sneezes and even breathes. The virus can live up to two hours in the air and on surfaces in a room where an infected person has been.

Someone infected can transmit the disease from four days before to four days after a flat, itchy, red rash shows up. Measles symptoms may not appear for a week to three weeks after exposure.

While Rockland County's overall vaccination compliance rate is 94 percent, Orthodox Jewish schools in the area vary widely in vaccination rates from 40 to 100 percent.

The World Health Organization considers herd immunity to be achieved when a community has 95 percent of its members vaccinated. This helps protect those who cannot receive vaccinations because they are too young, have immune system problems or are too ill to get the shots.

Nationwide in the 2017-18 school year, 94.3 percent of kindergarteners in 49 of 50 states had received both doses of the MMR vaccine, the CDC said.

The outbreak in Rockland County, about 25 miles north of New York City, is one of 11 outbreaks in 25 states reported so far this year. States affected are Arkansas, California, Connecticut, Florida, Illinois, Indiana, Kansas, Louisiana, Maryland, Massachusetts, Michigan, Minnesota, Missouri, Nebraska, Nevada, New Jersey, New York, North Carolina, Oklahoma, Oregon, Pennsylvania, Tennessee, Texas, Virginia and Washington.

South Carolina is not on the CDC's most recent list; however, three cases have been confirmed in the past week in Spartanburg County, according to the South Carolina Department of Health and Environmental Control. Three or more linked cases constitute an outbreak.

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Rockland County's measles outbreak and cases in New York City – and Bergen County and Lakewood, New Jersey – have been linked to Israel.

An 18-month-old unvaccinated girl died from complications of measles Thursday in Jerusalem, the country's first measles death in 15 years, according to The Jerusalem Post. Nearly 1,300 cases in the country of 8.5 million residents have been reported so far this year; in contrast, the United States has about 329 million people.

Meanwhile, an outbreak in Europe has left more than three dozen dead.

General skepticism about vaccinations, including the MMR shots, continues among some, no matter where they live.

This questioning of vaccines plays out in different ways, though. Some swear off all vaccines, believing they carry more risks than the diseases they are designed to fight.

Other parents remained concerned about what they see as an overwhelming and aggressive vaccination schedule.

They may want to slow the amount of shots given or skip certain inoculations. In a vacuum, they may opt out of vaccinations because they don't think their ideas will be welcome.

Ruppert said she's been talking with families who are "in between," who focus on delaying a vaccination schedule. She has found them amenable to education and explanation if their concerns are respectfully addressed.

Part of today's problem has been the success of childhood immunizations in previous generations, said Zucker, who is a pediatrician with a subspecialty in critical care. People aren't familiar with many of the diseases that killed or maimed children as few as 25 years ago; the chicken pox vaccine was introduced in the United States in 1995.

"I've seen these diseases, all of them, diptheria to measles," he said. "I've seen the measles encephalitis, I've seen whooping cough. I don't think any parent would want to experience that with a child.

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"I recognize the worries of this," Zucker said of parents' concerns. "But I recognize the need for vaccinations."

Because the vaccinations prevent diseases, they don't see what could happen, he said.

Complications of measles include pneumonia, brain damage, deafness and death. The disease can be dangerous, especially for babies, young children and pregnant women who haven't had the virus.

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A clinic Friday in Monsey, New York, drew 99 people. One child was turned away because he showed symptoms of measles, Ruppert said.

"If they're looking sick, they don't come in the building," she said, explaining that every person is given a quick analysis at the door so anyone infected doesn't end up spreading the virus at the clinic. She was gratified that the parents of the sick child decided to have the siblings receive the vaccine anyway.

Contributing: Liv Osby, The Greenville (S.C.) News; USA TODAY. Follow Nancy Cutler on Twitter: @nancyrockland