This year's flu shot is protecting about half of Americans who were vaccinated, which suggests the vaccine is providing moderate levels of protection, STAT reports.
Interim CDC estimates show the vaccine offers about 47 percent protection against all flu infections and 46 percent protection against H1N1 viruses, which are causing most of illnesses this year across the U.S. The vaccine's protection rate against H3N2 viruses, which are prevalent in the Southeast, is 44 percent.
In other words, for every 10 flu infections that occur among unvaccinated individuals, four or five would have been averted if they'd gotten the flu shot.
This flu season has been mild, with fewer infections than last year, meaning the CDC has less data available to use for calculating the interim estimate, Alicia Fry, MD, head of epidemiology and prevention in the CDC's flu division, told STAT.
But Dr. Fry called the signs of vaccine effectiveness so far "encouraging," adding that the flu shot's protection rate is within the range of what one would expect during a flu season when H1N1 viruses predominate.
This season's vaccine is also an improvement over the 2017-18 season, when the mid-season estimate of how the vaccine was working showed about three-quarters of people who got the vaccine were not protected against H3N2 viruses, which caused the most illness last year.