Public health officials in Israel are urging crew members on national air carriers to ensure that they have received the proper dosage of the measles vaccine after a flight attendant contracted the deadly disease, possibly in New York.

Officials with Israel's Ministry of Health said a 43-year-old flight attendant for the national airline El Al had flown back to Israel late last month from John F. Kennedy International Airport in New York. New York state has been a battleground for concurrent measles outbreaks in Brooklyn and Queens as well as in Rockland County. However, because of the woman's "impaired mental status," officials said it could not be confirmed where or when she contracted the virus.

Eyal Basson, a spokesman for Israel's Ministry of Health, told The Washington Post that the woman, who is believed to have been vaccinated as a child, was admitted to the hospital March 31 and has developed encephalitis, a severe complication from measles that causes the brain to swell. As of Wednesday, Basson said in a statement, the woman was unconscious.

Itamar Grotto, associate director general of the ministry, told CNN that the woman has been "in a deep coma for 10 days, and we're now just hoping for the best."

Israeli health officials issued an alert earlier this month about a measles patient who had traveled on El Al Flight 2 on March 26 and 27 from New York to Tel Aviv. Officials told passengers and crew members to watch for symptoms and report them immediately to health care professionals.

El Al said in a statement to the Jerusalem Post that it "operates according to the Health Ministry guidelines."

"The Ministry issued precise instructions for all passengers on the flight. If you have any further questions, contact your family doctor or the Health Ministry," the airline said.

It does not appear that the patient spread the virus to others on the flight.

Basson said public health experts have not been able to speak with the woman because she is unconscious, but her mother told them that she had received all required childhood vaccinations, which, in the 1970s, would have included one dose of a vaccine intended to protect against measles and other childhood diseases. Israel now recommends two doses of the MMR/MMRV (measles, mumps, rubella and varicella) vaccine, but it's not known whether the woman received the second dose.

U.S. public health experts have said that one dose of the MMR vaccine is about 93 percent effective at preventing measles, an extremely contagious virus that can have serious consequences - pneumonia, hearing loss, brain damage and death.

The Post's Lena H. Sun reported that the Centers for Disease Control and Prevention recommends that children receive two doses of the MMR vaccine - the first at 12 to 15 months of age and the second at 4 to 6 years of age.

Sun added:

"People born between 1957 and 1989 generally only had one MMR dose. One dose is about 93 percent effective at preventing measles, but anyone in that age group can still get a second dose, says Russell Faust, medical director for Michigan's Oakland County health department."

" 'There's no downside to getting an MMR, especially during an outbreak," says Faust."

Since the introduction of the measles vaccine in the 1960s, measles cases in Israel, as well as in the United States, have declined steadily.

But in recent years, amid worldwide measles outbreaks and an anti-vaccine movement - sustained, in part, by fraudulent research that purported to show a link between autism and a preservative used in vaccines - the numbers have spiked. From March 2018 to January, more than 3,400 people have been infected with measles in Israel, the Health Ministry said.

The recent outbreak there has largely affected the country's ultra-Orthodox Jewish communities, within which there has been more reluctance to vaccinate children, according to the Times of Israel.

The United States also has been battling such outbreaks.

In 2000 - almost four decades after parents began vaccinating their children - measles was declared eliminated in the United States, according to CDC data.

But CDC data shows that from 2000 to 2018, there were 140 measles cases on average per year in the United States. And three fatalities were reported during that time - one in 2002, one in 2003 and one in 2015.

Over the past three months, according to the CDC, 555 measles cases have been reported in 20 states, including Oregon and Washington.