WASHINGTON, Feb. 20 (Xinhua) -- This year's flu season in the U. S. has hit younger- and middle-age adults harder than in the past three years, as a result of the resurgence of the H1N1 virus that caused a worldwide pandemic in 2009, the U.S. Centers for Disease Control and Prevention (CDC) said Thursday.

　　People aged 18 to 64 represented 61 percent of all hospitalizations from influenza, up from the previous three seasons when this age group represented only about 35 percent of all such hospitalizations, the CDC said.

　　Influenza deaths followed the same pattern with more deaths than usual occurring in this younger age group, said the CDC, failing to provide an exact number of deaths caused by the flu.

　　"Flu hospitalizations and deaths in people younger- and middle- aged adults is a sad and difficult reminder that flu can be serious for anyone, not just the very young and old," CDC Director Tom Frieden said.

　　The CDC urged that everyone should be vaccinated as a CDC study, also released Thursday, found that flu vaccination may reduce a person's risk of having to go to the doctor for flu illness by about 60 percent across all ages.

　　It recommends that everyone six months and older get an annual flu vaccine. "The season is still ongoing. If you haven't yet, you should still get vaccinated," said Frieden. Typically, the flu season ends in March or April in the U.S..