Nearly half of adults hospitalized in the U.S. for flu so far this season have been obese, much higher than in other recent flu seasons, according to the Centers for Disease Control and Prevention.
USA Today reports that 46 percent of adults hospitalized for influenza as of Jan. 4 were obese.
In previous years, the percentage of obese patients hospitalized for flu was in the 20-30 percent range, according to health authorities. Being overweight is a risk factor for having a less efficient immune system, which can make people vulnerable to infection.
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Pregnant women also appear to be getting hit hard by this season's flu, say experts. Researchers aren't entirely sure why these groups may be so strongly at risk, but believe it might be linked to immunological effects. Both obesity and pregnancy are known to alter the immune response. They also both tend to result in respiratory restrictions.
Most of the cases in the U.S. are the H1N1 flu strain, which caused a global pandemic during the 2009-2010 flu season.
Overall, this year's flu strain seems to be hitting younger people, pregnant women, people with chronic disease and the obese hardest.