Why this year's flu season is hitting hard

Expert says severe strain is partially to blame

ANN ARBOR, Mich. – Inside the Flu Lab at the University of Michigan School of Public Health, samples from local patients are coming in at a rapid pace.

It's one of five sites nationwide working with the Centers for Disease Control and Prevention to help determine how effective this year's flu vaccine really is.

"We really have an active flu season, and we're in the middle of it right now," Dr. Arnold Monto said. "We think we are close to the peak, but that is always hard to predict until you start going down from the peak."

Monto is a world renowned expert in influenza. He says the predominance of H3N2 this year is partially to blame for the severe season.

"We're seeing mainly A H3N2, seeing lots every day. This particular subtype, unfortunately it both causes the most severe disease in terms of complications and it also is the one that the vaccine doesn't work as well as the other subtypes," Monto said. "We know why, but fixing the problem is not easy."

Monto believes a large part of that challenge has to do with how the flu vaccine is currently made.

"The reason it happens is that the vaccine virus is grown in eggs. When you put the vaccine virus into eggs, there are mutations in the virus and it gets to be less similar to the virus that's circulating in people," Monto said.

While researchers are working on other ways to grow the vaccine virus, for example, in insect cells or plants, Monto thinks incremental changes can also lead to a more effective vaccine.

"We really need to focus on the short-term as well as the long-term, and I think that's happening," Monto said.

One example of that is the high-dose flu shot currently approved for seniors.

It's about 20 percent more effective than the standard flu shot, and that includes higher protection against the more dangerous H3N2 strain.

Another advance is antiviral medications.

"We do have antivirals that are under-used when you do get the flu, and this is whether you are vaccinated or not," Monto said. "You do need to get the antivirals early, the earlier the better."

While this flu season is still going strong, Monto says the FDA will be meeting on March 1st to formalize the strain selection for next year's flu vaccine. That timing gives you an idea of why it's so challenging to create a vaccine for this moving target.

In about a month, researchers at the Flu Lab will have preliminary data on how effective this year's vaccine has been. Monto can already say it's been a strange flu season.

"A lot of people are getting sick that haven't got flu in a long time," Monto said.