Federal public health officials are investigating a “large and sudden” outbreak of the flu among students at the University of Michigan, the university announced this week.
Since October, there have been 528 cases of the flu on the campus in Ann Arbor, a vast majority — 77 percent — occurring in students who have not been vaccinated against the flu. The spread of the disease has accelerated over the past several weeks, according to the university.
Experts from the federal Centers for Disease Control and Prevention were on campus this week to assist university officials and the local health authorities in analyzing the outbreak and assessing the effectiveness of this year’s flu vaccines.
Emily Martin, an associate professor of epidemiology at the university’s School of Public Health who is assisting with the investigation, said the current case count was significant, especially compared with those of recent years. She added that the university might be identifying more flu cases this year because students were seeking tests for symptoms that overlap with Covid-19.
“It’s a great opportunity to get a good early signal on what vaccine effectiveness is right now, what strains are circulating, what it could forecast for the rest of the country,” Dr. Martin said.
Nationally, the flu infection rate remains low, but the C.D.C. said this week that it had received reports of spread among college-age adults. Outbreaks such as the one at the University of Michigan represent the “first significant” activity of this year’s flu season, the agency said in a statement. Flu season generally begins in October and can last through May, the agency said.
The University of Michigan outbreak is the only college campus investigation that the C.D.C. is currently involved with, said Kate Grusich, an agency spokeswoman.
The university and the local health authorities requested the agency’s aid, Dr. Martin said, adding that the investigation was a joint effort.
In Michigan, 2.2 million doses of flu vaccine have been administered this year, a figure that represents about 22 percent of the state’s population, according to state data. Vaccination rates have lagged in every age category compared with those of the previous two years.
In Washtenaw County, which includes Ann Arbor, about one in three residents is vaccinated against the flu, data shows.
An estimated 43.2 million flu vaccinations had been administered nationally in pharmacies and doctor’s offices to people 18 or older by the end of October, Ms. Grusich said. About 62.4 million doses were administered in the same time period last year, she said.
Experts said that last year’s flu season was mild compared to those of previous years, as the precautions that people took to slow the spread of the coronavirus, including masking and social distancing, helped prevent the spread of the flu.
Dr. Martin said the university was hearing from students who were confused about how the flu vaccine and the Covid-19 vaccines might interact. She encouraged students to get both vaccines, emphasizing that they have distinct benefits.
“One doesn’t replace the other,” she said.
A recent survey by the National Foundation for Infectious Disease found that four of 10 Americans were unsure about the flu vaccine or did not plan to get it. About a third of the 1,000 people surveyed reported having greater concerns about getting Covid-19 than the flu.
But experts cautioned that this year could be different and that little is known about the interaction of Covid-19 and the flu. The C.D.C. recommends that everyone age 6 months or older get a flu vaccine.