As the U.S. flu season winds down, health officials say the flu vaccine didn’t work very well, with one of its worst effectiveness rates in more than a decade.

A new strain that dominated the early winter was not well matched to the vaccine, leading to an intense early onslaught of flu.

The Centers for Disease Control and Prevention on Friday posted data that showed a continued decline in doctor’s office and hospital visits for flu symptoms through last week. The number of states reporting high flu activity dropped to 16, many of them in a belt stretching from Colorado to Virginia.