Boston health officials said Wednesday that along with an unusual second, late surge of flu cases across the state, the illness’s severity has also increased this season.

The Centers for Disease Control and Prevention estimates 19,000 people have died from the flu so far this winter, including 86 children. Thursday, the CDC reported at least nine of those children experienced brain complications, and it has asked state health departments to help investigate if there are more such cases.

The U.S. Centers for Disease Control and Prevention is investigating rare brain complications tied to the flu in kids This year’s flu shot reduced hospitalization risk by up to 78% in children Neurological symptoms in flu patients need immediate medical attention FRIDAY,

This year’s harsh flu season – the most intense in 15 years – has federal health officials trying to understand if it sparked an increase in a rare but life-threatening brain complication in children.