(Meredith/CNN) – It’s been one of the toughest flu seasons in years. Some people are at risk of catching the virus, even if they got a flu shot.
But how does that happen?
“Every year, it’s a bit of a guessing game to decide what strain of the virus gets put into vaccines,” Dr. Mark Rupp, who works at the University of Nebraska Medical Center, said.
In order to decide which strain of the virus to inset into the vaccine, researchers take a look at what strains of influenza are prominent in the Southern Hemisphere. This allows them to be more accurate when trying to predict how to handle the upcoming flu season each year.
However, this year, the problem was that the strain researchers chose, H3N2, doesn’t grow well in eggs, which is how the FDA requires vaccine viruses to be grown.
"The process for the virus to be adapted into the chicken eggs actually caused the virus to change a little bit and because of that change, the vaccine doesn't fully recognize the wild-type strain that's in circulation,” Rupp said. "We need to discover or to define a better universal target so that we don't have to change the vaccine from year to year, and this target has to allow for long-lasting immunity.”
Doctors still recommend every get a flu shot every year.