Flu Activity Now Widespread In Mass.; H1N1 Dominant Strain

BOSTON (CBS/AP) --Flu season appears to be in full swing in Massachusetts, with health officials reporting 860 cases statewide.

Health care providers are seeing an uptick in the H1N1 strain that was prevalent in 2009. H1N1 or "Swine Flu" typically causes more illness in children and young adults, compared to older adults, although severe illness is possible in all age groups.

The CDC says this year's vaccine does protect against the H1N1 strain.

The Center for Disease Control says hardest hit areas include Massachusetts, New York and Pennsylvania.

Flu is usually the worst in January or February, although last year the illness hit the U.S. very hard in early December.

According to the Centers for Disease Control and Prevention, last year's flu season landed about 381,000 people in the hospital nationwide. That's the most since at least 2005.

A contributing factor: The flu vaccine was only 51 percent effective overall.

The CDC released an alert on the H1N1 strain last week.

"While it is not possible to predict which influenza viruses will predominate during the entire 2013-14 influenza season, pH1N1 has been the predominant circulating virus so far. For the 2013-14 season, if pH1N1 virus continues to circulate widely, illness that disproportionately affects young and middle-aged adults may occur," the alert said.