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.

"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.

"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.