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NORTH BERGEN, N.J. — The family of a 6-year-old girl who died from a flu-related illness said their child had been vaccinated against the virus and believe that her death was preventable.

Nevaeh Hernandez died on Monday. She was a kindergarten student at Lincoln School in North Bergen.

“The flu is attacking our children and it’s worse than it’s ever been before,” Sandy Rivera, the child’s grandmother, said.

Rivera and her family all have medical training.

“She had the flu vaccine. We took her to the hospital. We are EMS. We weren’t naïve,” she said.

Stephanie Conteron, the girl’s mother, said her daughter started complaining about a headache last Friday. Later that day, she began to have a fever and Conteron took her daughter to Hoboken University Medical Center.

The family said they waited three hours to see a doctor, then were met by a nurse and a physician’s assistant instead. They said the Hoboken hospital failed to diagnose Hernandez with the flu and discharged her.

Within 24 hours, the girl’s temperature spiked to a dangerous 106 degrees. Her mom called an ambulance.

“If you feel that your child is not right, and only a parent knows that… stay there…,” Rivera said. “Request whatever you need. (Say,) ‘I don’t feel right I’m not going anywhere.’ Because we feel it could have been prevented.”

At Hackensack University Medical Center, staff diagnosed Hernandez with H1N1, the so-called swine flu, within two hours of their arrival.

But it was too late. Hernandez started having seizures.

The family has hired an attorney to explore a lawsuit against Hoboken Medical Center.

“The reason for this conference is to make sure parents know how deadly (this flu is). Seek medical attention immediately,” attorney Louis Zayas said.

He advised that caregivers insist that a child with flu symptoms remain under hospital observation for 24 hours and that they see a doctor.

Hoboken University Medical Center couldn’t comment on this specific case but said that they “meticulously follow all CDC guidelines and protocol related to the flu or possible flu cases.”

The CDC announced on Thursday that this year’s flu vaccine is 25 percent effective against the most common strain.

It is almost 70 percent effective against H1N1, the strain that Hernandez had, and it’s 42 percent effective against the influenza B virus.

Because of what happened to Hernandez, the city of North Bergen is offering an adult flu clinic next week. Students are getting in-school flu shots through next week.

Officials said it is not too late to get vaccinated, especially because flu season is expected to extend through March.

Hernandez’s family had tickets to take her to a Broadway musical in the city on Thursday. Instead, they are planning her funeral for this weekend.

“Something more should have been done,” her grandmother said.

The Centers for Disease Control is reporting 63 children have died in the United States this season due to flu-related symptoms or complications, as of the week ending Feb. 3. One out of every 5 of them had been vaccinated.