PORTLAND, Ore. — Oregon State University said Wednesday it will fight an outbreak of meningococcal disease by requiring students 25 and younger to be vaccinated against the disease by Feb. 15.

The university announced its decision after the Oregon Health Authority reported that an undergraduate has been diagnosed with the disease, the sixth case in an outbreak that began a little more than a year ago.

“We’re raising the bar, and that happens today,” university spokesman Steve Clark said.

The latest case is a 21-year-old student enrolled at the Corvallis campus who was hospitalized Dec. 17 with meningitis — a potentially lethal infection of the brain and spinal cord — while visiting family. Preliminary tests found meningococcal disease to be the probable cause, and additional testing will determine whether it’s the same strain of meningococcal bacteria that caused the other illnesses.

The first five patients all made full recoveries. Charlie Fautin, deputy director of the Benton County Health Department, said that’s statistically unusual, and the disease has fatality rate of about 10 percent.

Symptoms include the sudden onset of a fever, stiff neck and headache. It can also cause flu-like symptoms and nausea, vomiting and a rash.

“This disease can progress from sort of feeling like you have the flu — feeling kind of cruddy — to being catastrophic very quickly,” Fautin said.

Health officials urged students to get vaccinated during the winter break that began Dec. 9 and continues through Jan. 7. The university held three mass vaccination clinics this fall, but attendance was not mandatory.

The disease primarily afflicts young people and can spread in group living situations such as dormitories.

A University of Oregon student, Lauren Jones, died during an outbreak on the Eugene campus in 2015. A doctor at the hospital near campus diagnosed her with a flu-like illness and sent her home to rest. The 18-year-old woman died later that day in her dorm room.

A jury in September ruled that the hospital provided negligent medical care, and awarded $1.5 million to the student’s mother.