SALT LAKE CITY, UT – APRIL 26: In this photo illustration sterile water is prepared for a one dose bottle of measles, mumps and rubella virus vaccine, made by MERCK, at the Salt Lake County Health Department on April 26, 2019 in Salt Lake City, Utah. (Photo Illustration by George Frey/Getty Images)

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AUSTIN (KXAN) — A national surge of measles cases has health officials concerned about possible widespread outbreaks of the highly infectious disease.

As of May 3, there have been 764 cases of measles reported in the United States — the highest number of annual cases reported in 25 years. In Texas, there have been 15 cases of measles since the start of the year, according to the Texas Department of Health and Human Services.

A new study released by the University of Texas at Austin Friday predicts 25 counties in the United States have a higher risk for a potential outbreak based on a combination of low vaccine rates and high international travel.

In Texas, Travis, Harris, Tarrant and Bexar Counties all make that high-risk list. This aligns with a January study that included Austin, Houston, Fort Worth and Plano on a list of 14 U.S. cities that are hotspots for high non-medical vaccine exemption rates.

What’s in this map?

The Annual Survey of Immunization Status is a report published each school year by Texas. It reveals the vaccine exemption rates reported by school districts and some private schools.

Measles is a highly contagious disease and as a result, for “herd immunity” to work and prevent an outbreak, health officials believe at least 90 to 95% of the population must be immunized.

Texas allows parents to choose not to vaccinate their children for conscientious or religious reasons. Parents can fill out and submit a DSHS affidavit form to their child’s school. These are valid for two years.

The map below contains two sets of information:

The first layer reveals all the schools and school districts in Central Texas that reported their vaccine exemption rates in the 2017-18 school year.

The second layer reveals all the schools and school districts in Texas that reported their vaccine exemption rates as being higher than 5%, which is when “herd immunity” for measles vaccination is believed to stop working.

How to read this map:

Green markers represent schools/districts with under 5% exemption rate.

Yellow indicates an exemption rate between 5 and 10% that could leave the population vulnerable

Red indicates a high exemption rate above 10%

Black markers mean there was no exemption rate information available

Switch between the first layer with Central Texas data and the second layer with state-wide data, using the navigation bar on the left-hand side.

Limitations of this data:

This map draws from the 2017-2018 Annual Survey of Immunization Status conducted by state health officials.

The data is self-reported and although the report is mandated by law, not all schools participate each year. Also, schools with enrollment below 65 students are not included in the survey.

The total district exemption data is only reported at the district level so rates for individual public schools in Texas is not available.

The exemption rates reported on this map are the total conscientious exemption rates for the private schools and school districts. It is measured based on all the active exemptions the school or district has on file for kindergarten through 12th-grade students.

The exemptions may be to one or more vaccines. This data doesn’t include the breakdown of exemption rates for each individual vaccine. Those more detailed rates are only measured for the kindergarten and seventh-grade classes each year.

An exemption lasts for two years. Some students are on a delayed vaccine schedule and so parents opt for an exemption so they can attend school. If during the two years, a child receives the vaccine and parents don’t notify the school, the exemption remains active on file and so the rate may be inflated.

Resources for parents

Recommended vaccine schedule for children

Low-cost immunizations for children

Read about different vaccines, the diseases they combat and the symptoms