GALVESTON, Texas (KXAN) — Researchers in Texas have found a single mutation in the Zika virus, which they said could lead to a “major outbreak.”

Researchers with the University of Texas Medical Branch and La Jolla Institute for Immunology led a study together and made the discovery, according to university officials.

The study said with this single mutation, the “already rapidly evolving Zika virus” could bypass existing immunity.

The university explained one of the ways the virus can spread is through the bite of an infected mosquito. Right now, there’s no vaccine or medicine for Zika.

The Centers for Disease Control and Prevention said the virus can be passed from a pregnant woman to her fetus. This can cause birth defects.

Many people who contract the virus won’t have symptoms or will only have mild symptoms, including a fever, rash, headache, joint pain, red eyes and muscle pain, the CDC said.

Right now in the continental U.S., the CDC said there’s no current transmission of Zika. The last reported cases of the virus transmitted by mosquitoes in the country were in Florida and Texas in 2016 and 2017.

The full study on the Zika virus mutation is published online.