Texas cities are in danger of major measles outbreaks because an alarming number of school kids are unvaccinated, researchers warn.

Vaccination rates in the state have declined since 2003 and a computer simulation by University of Pittsburgh researchers found that an additional 5% decrease could increase the size of a measles outbreak by as much as 4,000% in some cities.

"At current vaccination rates, there's a significant chance of an outbreak involving more than 400 people right now in some Texas cities," study lead author David Sinclair said in a university news release. He's a postdoctoral researcher in Pitt's School of Public Health.

"We forecast that a continuous reduction in vaccination rates would exponentially increase possible outbreak sizes," he added.

At current vaccination rates, the simulation estimates that measles outbreaks of more than 400 cases could occur in Austin and Dallas-Fort Worth. This is because some schools have vaccination rates below 92%, low enough for the disease to spread.

If the vaccination rate dropped 5% in only the schools with low rates of immunized students, the size of potential measles outbreaks would jump sharply, the study warned. Outbreaks of 500 to 1,000 people could be possible in Dallas-Fort Worth, Austin and Houston, according to the study.

About 64% of cases would occur in kids who aren't vaccinated due to a religious or personal exemption. But the simulation suggests that 36% of cases would affect people with a medical condition that prevented vaccination; whose vaccine failed to trigger immunity; or in unvaccinated adults, who have a higher risk of complications.

Potential complications of measles include pneumonia, brain swelling and deafness. About one out of every 1,000 children infected with measles die from respiratory and neurologic complications.

The study was published online Aug. 21 in JAMA Network Open.

Measles is so contagious that, if no one were immunized, one person with the disease would likely spread it to 12 to 16 more. In comparison, one person with the flu infects one to two people.

The measles vaccine -- which is often combined with the mumps and rubella vaccines (MMR vaccine) -- provides 97% immunity after two doses, the researchers noted.

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