The U.S. Centers for Disease Control and Prevention says this is the worst flu season in the United States in 10 years, and the epidemic has not yet hit its peak.
Widespread flu is reported in 44 states, and the Centers for Disease Control says the percentage of people going to the hospital for treatment of flu symptoms has doubled in the past month. In some regions, hospitals are having to turn flu patients away.
The mayor of Boston declared a public health emergency Wednesday, with 10 times more cases reported than last year in the northeastern U.S. city.
U.S. health authorities say the flu arrived a month earlier than usual this year, in November, and the most prevalent flu strain -- H3N2 -- has a reputation for causing fairly severe illness, especially in the elderly.
The CDC recommends that everyone over the age of six months get a flu shot. In recent years, the vaccine has been about 60 to 70 percent effective at preventing the flu.