CDC completes Ann Arbor campus flu investigation

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An investigation into the sudden and large rise of influenza cases among students diagnosed in the last two months on the University of Michigan’s Ann Arbor campus has led to several recommendations from the U.S. Centers for Disease Control and Prevention.

The CDC is urging all individuals ages 6 months and older to be vaccinated to protect themselves from various strains this flu season and to seek testing if they become ill, and health care providers consider antiviral medication for flu prevention and treatment, especially in people at risk of complications from the flu.

The research team, which was led by the university in partnership with the Washtenaw County Health Department, Michigan Department of Health and Human Services and the CDC, has completed its initial analyses, and the CDC issued a report of the findings Dec. 3.

The collaboration continues as the team works to understand risk factors for influenza and immune responses to the vaccine and to infection.

A total of 745 flu cases — nearly all (99 percent) among the student population — were diagnosed at the University Health Service between Oct. 6 and Nov. 19. This represents some of the first significant influenza activity in the United States since March 2020. The majority of cases were mild and occurred in young, otherwise healthy people.

Findings show there were similar vaccination rates for individuals testing positive versus negative, suggesting that vaccination did not reduce the risk of flu illness associated with the specific strain of the A(H3N2) viruses found on campus.

However, officials noted the finding cannot be applied to other age groups, people in higher risk groups or other flu virus strains that might circulate this season, and emphasized the importance of getting vaccinated this flu season.

“The outbreak of influenza on campus serves as a reminder that flu can emerge and spread quickly, especially in certain settings,” said Emily Martin, associate professor of epidemiology at the School of Public Health and one of the U-M leads on the team.

“As the flu season is just getting started and we expect a number of strains to circulate, getting vaccinated is your best defense against flu and its potentially serious complications including hospitalization and even death.”

The H3N2 strain detected on campus has some genetic differences from the H3N2 component included as one of four strains in this year’s flu vaccine.

U-M is participating in ongoing work nationally to determine whether this will impact vaccine effectiveness for the 2021-22 season.

“Now that influenza is here on campus in addition to COVID-19, it is even more important to stay home when you are sick and contact your doctor for testing. There are medications available to treat influenza and to protect people that have been exposed and may be at risk of complications,” Martin said.

Officials also noted the study was not able to assess any attenuation of illness — meaning the severity of illness is lessened after vaccination so people aren’t as sick as they might otherwise have been if they were unvaccinated —  that may have resulted from vaccination.

Given the emergence of the flu alongside high levels of COVID-19 in the state of Michigan, the U-M community is encouraged to do the following​​ to stay healthy:

  • Get a flu vaccine (flu season can last from October-May).
  • Stay home if sick and seek care or testing, if needed.
  • Cover coughs and sneezes.
  • Wash hands frequently.
  • Get a COVID booster if you haven’t already done so.
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