As the flu season begins to wind down, many are coming to the realization that this year’s vaccine was not as effective as in years prior. That’s because the Center of Disease Control and Prevention (CDC) identified a new mutation in the dominant flu virus, leaving the vaccine only 30% effective.

“The CDC created the vaccine based on what was in the community at the time,” says pharmacist Dr. Leah Reinhard. “Shortly after, the flu virus made a shift, leaving the vaccine to be more ineffectual.”

The mutation to blame is called H3N2. Previous H3N2-dominant flu seasons have been associated with severe illness, according to the CDC.

“We still recommend that you get the flu shot, because it has been shown to decrease the severity of the illness,” says Kathryn Wall, the Public Health Information Administrator for the Greene County Health Department in Springfield, Mo. “But ultimately, the community must keep up with vaccinations in order to protect our children and those over the age of 65.”

While Wall says this year’s vaccine remains a good flu-prevention option, but it’s important to know that it will not fully protect as it has in years past.