(CBS) — This season’s flu outbreak has reached the epidemic level, and the Centers for Disease Control and Prevention reports it’s expected to get even worse in the coming weeks.

Fifteen children nationwide have died of influenza since the 2014-15 flu season began this fall. The number of people being hospitalized for the flu is also on the rise, with those age 65 and older especially at risk.

The CDC says 22 states are seeing high levels of illness — including Illinois, Indiana, and Wisconsin — up from 13 states a week earlier.

And the flu’s geographic reach is increasing too, with widespread cases reported in 36 states.

Dr. Scott Dresden of Northwestern University says the hospital started seeing flu case in mid to late November.

“The numbers have reached epidemic proportions, which isn’t surprising for this time of year, it’s just a little bit earlier than we usually see it,” Dr. Dresden said.

Last year: flu cases starting popping up in January, this year, almost a month and half earlier.

“It may be that we have an early spike and it fizzles out earlier or it may just be a longer, tougher flu season,” Dr. Dresden said.

Health officials are encouraging people to get a flu shot even though this year’s vaccine formula does not offer as much protection as usual. A prevalent strain of the virus this year, H3N2, mutated enough that it’s no longer a close match for the vaccine developed to block it.

CBS News chief medical correspondent Dr. Jon LaPook said that because of this mismatch, the current flu vaccine will probably be about a third less effective than normal.

Read more at CBSNews.com