Despite influenza A being the predominant strain of past flu seasons, influenza B is leading in case volume this year, and experts say that people in their mid-20s and younger are more susceptible to the virus.

Experts do not currently know the cause for the shift in predominance from influenza A to B, said David Kusner, infectious disease physician at Mercy Iowa City. Viruses often make changes in their nucleic acid recombination, he said, and fluctuate depending on how they’re selected by immune responses for either humans or animals.

Children and the elderly are the primary groups at risk, he said, but recently young adults up to about age 25 have also become more susceptible to influenza B, he said.

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Several variables can make some people more susceptible to one strain of influenza than the other, Kusner added, making the B strain more predominant this flu season than it has been in the past.

“Sometimes when [individuals] have past exposure, that might give [them] a partial immunity to it,” Kusner said. “That’s what we’re seeing now with influenza B where older people are not getting it very much, but younger people are.”

At Mercy Hospital, people are only mildly concerned about influenza B’s predominance. The primary concern is actually how to bounce back from last year’s tough flu season, Kusner said, because of a high rate of hospitalizations and even deaths. Mercy’s main focus is to not grow complacent as flu season progresses.

University of Iowa Health Care Infection Preventionist Stephine Holley said there’s a concern for influenza every year, regardless of a strain’s dominance, and that the hospital takes tremendous efforts to prepare for flu season.

“We put much effort into prevention strategies including promoting vaccination, identifying ill people and putting practices into place to minimize spread, encouraging good hygiene practice and, of course, monitoring the situation closely,” she said. “We have multiple teams that collaborate to ensure we are providing a safe environment for our patients, visitors, and staff.”

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In an email to The Daily Iowan, UI Student Health Medical Director Jennifer Johnson said the university has yet to see an abnormality in the number of flu cases at this point in the semester, but that health providers there have noted the unusual change in predominance of influenza strains.

Generally, influenza B becomes the prevalent strain in the later part of the flu season, Johnson said, so the early shift to influenza B prevalence is indeed out of the ordinary.

Student Health encourages students to pay close attention to what could be a more severe flu season, she said.

Johnson added that the best way to combat this change within the university community is to keep up healthy practices such as reducing stress, sleeping and eating well, and exercising. She also emphasized the need for students to get a flu shot.

“It’s not too late to get one,” Johnson said. “The more students who get a flu shot, the more it protects our entire campus [herd immunity], which makes it safer for people who can’t get a flu vaccine [such as babies under six months].”