- CDC figures show this season's flu vaccine is 47 percent effective.
- The predominant strain of flu virus this year is H1N1, which is less severe than last year's main strain.
- A CDC official says the number of deaths is "a little bit surprising."
The current flu season has been milder than last year's, with the vaccine protecting about half the people who were inoculated and a less severe strain of the virus causing most of the illnesses that do occur.
However, there have been more deaths than usual from that milder strain, and there is evidence a more severe strain of the influenza virus is causing a growing percentage of illnesses.
The current flu season started at the beginning of October and lasts until May. As of Feb. 2, between 13.2 million and 15.2 million people nationwide have caught the flu, the Centers for Disease and Control reported. There have been 9,600 to 15,900 deaths so far.
The CDC said the flu typically kills 12,000 to 56,000 people in the U.S. in a year.
“The number of deaths we’re seeing is a little bit surprising,” CDC epidemiologist Brendan Flannery told the Wall Street Journal. “It’s a reminder that flu can be severe.”
This year's vaccine, formulated for the H1N1 strain of influenza virus, has been 47 percent effective so far, the CDC also said. Last year's vaccine was 36 percent effective at the same point in the season. Overall, the 2017-2018 vaccine was 40 percent effective for the entire season.
About 90 percent of the cases tested by the CDC this season are the milder H1N1 strain of flu, NBC News reported. Ten percent are the H3N2 strain that was prevalent last season.
As many as 186,000 people have been hospitalized with flu this season, and most of them have H1N1 flu.
Health officials are seeing evidence that the H3N2 virus is causing a growing proportion of flu cases.
Dr. William Schaffner, a Vanderbilt University infectious diseases expert, told the AP that's unusual and it's not clear why that's happening.