It started with one case a few weeks ago.
Now a second East Lansing ninth grader has come down with pertussis, commonly known as the whooping cough.
"We felt that this constituted an outbreak situation for us," said Dr. Dean Sienko, medical director for the Ingham County Health Department.
He says the highly-contagious infection can be fatal for very young children. While not as serious for teenagers and adults, it's still dangerous.
"It can even be so strong that it breaks people's ribs they're coughing so hard," Sienko said.
Serious as it is, the health department and the high school alerted parents like Penny Barker Wali who has son in ninth grade at East Lansing.
"I was pretty concerned," Wali said. "I want to make sure he receives the vaccination."
Parents like Wali are in luck: the high school and the health department will immunize some students this week.
"We'll do half of the students on Wednesday morning and the other half on Thursday morning," East Lansing High School Principal Paula Steele explained.
But that's only ninth graders, some tenth graders who have classes with 9th graders and the teachers who teach them. Eleventh and twelfth graders won't be getting the vaccine.
"There is a limited supply of this vaccine nationwide so we have to apply the most effective use of resources," Sienko said.
A recent rise in reported adolescent and adult cases made the pertussis vaccine part of the regular tetanus booster about a year ago, so those who won't be getting the vaccine at school can see their doctor or the health department for a shot.
In the meantime, the department and the school will be keeping a close eye on school absences and on the students themselves.
So will parents.
"I'll be looking for some of those symptoms," Wali said.