Mumps outbreak in Texas reaches 23-year high At least 221 people have been diagnosed with mumps in Texas.

 -- Texas health authorities are trying to combat a record-breaking outbreak of mumps that has swept through the state.

The Texas Department of State Health Services reported there have been 221 cases of mumps in the state this year, the highest number since 1994 when 234 cases were reported. College students in particular have been among the hardest hit by the virus, which spreads through close personal contact and can result in swollen glands, fever and headache.

"State, regional and local health departments are currently investigating multiple outbreaks throughout the state, including one involving possible exposures on South Padre Island, a popular spring break destination," the health department said in a statement.

Texas is just the latest state to be hit with a large mumps outbreak. Last year the U.S. had multiple outbreaks of the mumps resulting in 5,748 total reported cases. Comparatively there were just 229 cases in 2015. Washington state has has 756 mumps cases since the start of an outbreak last October.

Dr. William Schaffner, an infectious disease expert at Vanderbilt University Medical Center, said unlike other outbreaks of diseases like measles, the recent mumps outbreaks appear to be occurring in populations with high vaccination rates.

"Although people are vaccinated, after about 15 years there is some waning of immunity and if you get a strong exposure that exposure can overcome that diminished protection and you'll get a case of mumps," said Schaffner.

People are usually immunized against mumps as children when they get two doses of the MMR (measles, mumps, rubella) vaccine.

Schaffner said college students are at particularly at risk since they live and go to school in close proximity to others. Additionally if they travel together for spring break, football games or other events the virus can spread from school to school.

"The college environment is such that it provides so many opportunities for close face to face exposure," he explained.

In a statement to ABC News last month, officials from the U.S. Centers for Disease Control and Prevention said the Advisory Committee on Immunization Practices (ACIP) plans to examine why mumps cases are increasing and determine if a third dose of the mumps vaccine during an outbreak could help prevent the virus from spreading.

"CDC is investigating the factors that may be contributing to the increase in cases, including that the vaccine prevents many but not all cases of mumps; the disease spreads more easily in crowded settings; and the possibility that the protective effect of the vaccine decreases over time," the CDC said.

Schaffner said in recent years epidemiologists have wondered if the virus has mutated enough that the current vaccines are not effective enough at providing protection, although he clarified that it's far too early right now to know for sure.

"You can see minor variations and the question is, is that enough to evade the protection provided by this vaccine?" he said.

The CDC said last month that the vaccine continues to work well in children and pointed out that prior to the mumps vaccine there were approximately 186,000 cases of the virus annually in the U.S.

"Since the pre-vaccine era, there has been a more than 99% decrease in mumps cases in the United States," the CDC said.

The mumps virus is spread through close personal contact and through coughing, sneezing, or talking. While most people infected with the virus recover without serious complications, in rare cases the virus can cause swelling of the testes, the ovaries, the membrane surrounding the brain and the brain itself.