US health officials vowed Thursday that this year's vaccine against influenza is better than last year's, which packed little punch against the most common strain of the virus.

Everyone over the age of six months is urged to get the annual flu vaccine in order to prevent serious illness and death, the US Centers for Disease Control and Prevention said at a press conference in the US capital to mark the beginning of flu season.

"Flu is unpredictable but you can predict that the single best thing you can do to protect yourself is to get the vaccine," said Tom Frieden, director of the Centers for Disease Control and Prevention.

"The vaccine has been updated to better match the H3N2 strain," added Frieden, urging pregnant women, older people, children and health care workers in particular to make sure they get vaccinated.

"Even in a good year -- 'good' in quotation marks -- flu will result, in this country, in millions of cases of illness, hundreds of thousands of hospitalizations and thousands or tens of thousands of deaths."

Last season, the predominant flu strain was H3N2, sometimes referred to as the Switzerland variant, and the vaccine was not well equipped to fight it because it emerged after the vaccine had already been mass-produced, he said.

The 2014-2015 season had the highest hospitalization rate among seniors that the CDC had ever documented.

The predominance of the H3 flu strains last season made the illness particularly serious for seniors.

There were also 145 documented deaths from the flu among children, though the actual number is suspected to be higher, Frieden said.

Overall the flu vaccine is usually 50-60 percent effective.

Last year's effectiveness was "quite low," and offered only about 13 percent protection against the common H3N2 strains, while the H1N1 and B strains were protected at a rate of 50-60 percent, Frieden said.

About half of the US population got the shot last year, he added, expressing hope that even more people will get vaccinated this year.

"Now is a good time to get a flu vaccine," Frieden said.