AMHERST — Two University of Massachusetts Amherst students hospitalized to treat a potentially deadly meningococcal disease have a strain of the illness students are generally not vaccinated for.

“We have received confirmation that the diagnosis for the second student is Serogroup B. This is a confirmation that UHS had anticipated,” University Health Services Executive Director George Corey said in an email to campus on Wednesday. “UHS continues to work in consultation with federal and state public health officials.”

The first UMass student to become ill with the disease was diagnosed Oct. 24 and was initially in critical condition. That student was diagnosed with the Serogroup B strain. Three weeks later, the university announced on Tuesday a second person was ill, though it was unclear if student was also suffering from the Serogroup B strain.

“As a precaution, students may want to receive the Serogroup B vaccine. The vaccine is available at UHS by appointment,” Corey wrote in his email. “Please call 413-577-5101 between 8 a.m. and 5 p.m. to schedule an appointment. Costs for vaccination are billed to your insurance company. Please bring your insurance card to your appointment.”

By Wednesday afternoon, some 100 students had visited University Health Services to receive the first dose of a vaccine to protect against Serogroup B. The meningitis vaccine required to attend the university only covers strains A, C, Y and W.

Meningococcal disease refers to illness caused by bacteria called Neisseria meningitidis. When the infection occurs in the brain and spinal cord, it is called meningitis. The bacteria can also cause blood infections. Even with treatment, 10 to 15 percent of people with the disease will die, according to the Centers for Disease Control and Prevention. Up to 20 percent of survivors suffer long-term disabilities like deafness, brain damage or amputations.

Meningococcal disease often occurs without warning and must be treated right away. The university raised its level of concern because the infected students were not in close contact. Both are hospitalized in stable condition.

“UHS continues to encourage students to consider making an appointment with their family health care provider if they are going home for Thanksgiving break to receive the vaccine,” UMass spokesperson Mary Dettloff said in an email Tuesday. “The vaccine is a two-shot vaccination and requires that students return for the second vaccine in 30 days.”

More than 21,000 undergraduates attend UMass Amherst and 77 percent of them live in the state, according to the university’s website. Many students will head home over the weekend as residence halls close for a week-long Thanksgiving break.

UMass officials did not say Tuesday night whether they consider the situation an outbreak or anticipate additional cases. The Centers for Disease Control and Prevention says an outbreak occurs when multiple cases of the same strain happen in a short time period.

“Depending on the population size and specific circumstances, health officials may declare an outbreak after just two cases,” the centers say. Outbreak control measures include vaccinating people at increased risk of contracting the disease and giving preventative antibiotics to those who were in close quarters with an infected person. The university has taken both precautions.

Dettloff said the university has enough vaccines available to meet “ongoing demand.” The Serogroup B vaccine is relatively new. It was licensed by the Food and Drug Administration in late 2014. The vaccine does not take effect immediately. The university told students to avoid coming into contact with saliva — which is how the bacteria spread — by not sharing food or drinks and washing hands frequently.