A four-year-old girl in Iowa who didn't get vaccinated this season was left blind after getting the flu — and her parents said doctors don’t know if she will ever see again.

Jade DeLucia’s mother took her to the hospital on Christmas Eve when her fever became dangerously high.

Doctors fear 4-year-old Jade DeLucia may never see again because of the flu. She was rushed to the hospital on Christmas Eve and developed a swelling of the brain that caused her to lose her vision. Nightly News

“I looked down at her and her eyes were in the back of her head,” Jade’s mom Amanda Phillips told NBC News.

The four-year-old spent more than two weeks in the hospital, her mom said, and developed a disease called encephalopathy, a swelling of the brain that caused her to lose her vision.

This encephalopathy complication is not just relatively rare, it’s very, very rare; .21 per million is about 1 in 5 million.

Doctors told Phillips they won’t know if her daughter’s vision loss is permanent for six months.

Phillips said she got her daughter vaccinated last March, and hoped that would work for the current season, but doctors say it's crucial to get the vaccine in the fall before each season.

This season’s flu strains are hitting children particularly hard, the Center for Disease Control said Friday. Two different flu strains are widespread, and there are twice as many pediatric flu deaths so far this year than at the same time last year, the CDC said.

The agency estimates that at least 9.7 million people have had the flu this season, with 87,000 hospitalizations and 4,800 deaths reported so far.

Phillips hopes Jade’s story gets parents to take the flu seriously.

“You do what's best for your children,” she said. “You know your children."