Boston declares public health emergency for flu outbreak

As of the last week in December, the Centers for Disease Control (CDC) reported that 41 states are experiencing "widespread geographic influenza activity," a sharp increase from the week before.

The share of people seeing doctors for flu-like symptoms recently hit 5.6 percent nationally, more than double the peak proportion from last year, the CDC said.

Residents of Boston can receive free flu vaccines at city health centers.