Since January, the U.S. Centers for Disease Control and Prevention have identified 764 measles cases — the most since a 1994 outbreak — mainly due to outbreaks in places like Los Angeles, Washington and New York City.

Although declared eliminated in the U.S. 2000, the disease has come roaring back. But is an outbreak likely here? According to work by University of Texas and John Hopkins University researchers published Thursday in the journal Lancet Infectious Diseases, the answer is yes.

The researchers have identified the 25 U.S. counties most at risk for an outbreak, and Travis County is No. 22. The county ranks there mainly because of its low vaccination rates, said lead researcher Sahotra Sarkar, a UT professor of integrated biology and philosophy.

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Travis County has the 13th highest vaccination opt-out rate in the country, according to a 2018 public health study. Among the 25 schools in Texas with the most kindergartners not inoculated against measles, six are located in Central Texas, state health data show.

Researchers said they were surprised by the degree that travel, particularly international travel, affected the risk of a measles outbreak. It helped push Chicago's Cook County, Ill., to No. 1, ahead of Los Angeles County at No. 2 and Miami's Dade County at No. 3. Other Texas counties at risk include Houston's Harris County at No. 9, and Fort Worth's Tarrant County at No. 12. The online index has a total of 50 counties on it, and San Antonio's Bexar County is No. 33

Measles outbreaks are happening in the Philippines, China and India because of a lack of access to vaccines, Sarkar said. Outbreaks in the U.S., as well as Italy, France and other European countries, are driven by low vaccination rates.

While Austin-Bergstrom International Airport doesn't have many international flights, international travelers do come here for the University of Texas, the state government and to visit the Hill Country, Sarkar said.

"If a single case occurs," Sarkar said, "it could spread very, very fast because of number of people that haven't been vaccinated."

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Measles is a highly contagious airborne disease that spreads quickly if you are standing anywhere near an infected person. Most of those infected don't die, but they do develop symptoms that include high fever, cough, runny nose, red eyes and white spots in the mouth, as well as a rash that spreads from the head down the body, usually on the third to fifth days of the infection.

Those most at risk of serious complications, such as encephalitis and death, are the very young, the very old and those with suppressed immune systems that can't fight off the disease.

The measles vaccine is very effective, Sarkar said. It's typically given to 1-year-old children and again at 4 years old. If you've had both doses, he said, "then you're very likely to be immune." But he advises those traveling overseas to check with their doctors.

Sarkar recommends giving children in areas at high risk of outbreaks three shots: one at 6 months old, the second at 1 year old and the third at 4 years old. High-risk areas like New York City already have encouraged this switch to three shots.

While measles in the U.S. has not been classified as endemic as it is in other countries, it could if the current outbreak continues for more than a year, Sarkar said. The number of cases so far this year already surpasses the 667 cases reported in 2014, the year of the last outbreak, and Sarkar suspects it will surpass the levels of 1994 when there were 958 cases. He doesn't think it will reach 1992 levels of 2,200 cases.

Measles isn't the only threat posed by low vaccination rates. Travis County has recorded recent cases of mumps and pertussis, also known as whooping cough.

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For years, anti-vaccination proponents touted a study by Dr. Andrew Wakefield, who worked in Austin, that linked vaccines to autism. That study has never been replicated and has been debunked.

"It's very clear by now that whatever happens in the brain that leads to autism happens long before vaccination," Sarkar said.

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Sarkar said side effects also are given as reasons not to vaccinate, but they shouldn't be. "There's never a guarantee, but the side effects are very rare. They're very mild," he said, and typically include fever and redness at the site of the shot.

Travis County and the other areas researchers identified as at risk of a measles outbreak should be identifying potential hot spots, such as schools with low vaccination rates, Sarkar said.

"In communities like that, if we do see measles, we need to be strict," he said, which could mean enforcing quarantines that ban the nonvaccinated from public gathering places, such as concert venues, movie theaters and libraries.

Sarkar said he's sensitive to civil liberty concerns but not at the expense of public health. "For the health of the community," he said, "there are things we need to do."