Flu Vaccine Effective in Fewer Than 1 in 4 in U.S.

This season’s flu vaccine is just 23 percent effective against the illness, further evidence that the inoculation was mismatched to the viral strains that eventually infected Americans.

The vaccine’s effectiveness “is relatively low compared with previous seasons, when circulating viruses and vaccine viruses were well matched,” the Centers for Disease Control and Prevention said in an early estimate published today. The agency was able to make an estimate early in the 2014-2015 season because the flu has reached an epidemic level faster than in recent years.