Flu Activity Worsens Nationwide, CDC Reports

— -- The 2014-15 flu season continues to be especially bad in the United States, with 43 states now reporting either high or widespread flu activity, according to the latest flu surveillance report released today.

This year's predominant flu strain, called H3N2, is partially to blame for the bad flu season, accounting for 95 percent of all cases reported, according to the Centers for Disease Control and Prevention. This strain is associated with more severe illness and more deaths.

On top of that, this year's flu vaccine is considered a "very bad match" for the H3N2 strain, Dr. Richard Besser, ABC News chief health and medical editor, said.

"People say put those together, and it could be a very bad year," Besser said.

This year's flu vaccine isn't as effective as in years past because the virus mutated after the shot was developed and manufactured, said Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases. As a result, it's only 33 percent effective at preventing the flu.

Still, he said, it's wise to get the flu vaccine anyway because it offers more protection than not getting the shot at all. Adults older than 65, children younger than 5, pregnant women and those with medical conditions, including asthma and liver disorders, are at the highest risk for developing flu complications and should be sure to get the shot as soon as possible.

Hospitalizations from flu-like symptoms have climbed to 5.9 percent, and 21 children have died from the flu since the flu season began.

The flu season started early this year, Fauci said, and although it usually tapers off a bit around the holidays, when people stay home from the office, that didn't happen this year.

"The one thing about the flu that you can be sure, it’s really unpredictable,” Fauci said on ABC News’ “This Week” Sunday. “At the end of the day, it just devolves and it’s difficult to predict.”

As of Dec. 27, this year's flu levels are "almost even" with peak levels from the last time H3N2 was the dominant strain, in 2012-13, according to today's report.

The Southern states and the Midwest have been hit hardest so far, and the flu is expect to reach higher activity levels in other parts of the country before the flu season ends, the report reads.

"Most of the Northeast and West of the country has yet to experience the full brunt of the flu season," according to the CDC report.