Ayzlee McCarthy spent much of Dec. 26 playing with Christmas gifts and trying on her new "Frozen" dress-up clothes.

Three days later, the feisty 3-year-old was dead, the cause attributed to complications from influenza.

"She was healthy. She had a flu shot," said Amber McCarthy, Ayzlee's mother. "The whole thing is so unreal."

Preliminary data show that three Iowa children, ages 17 or younger, have died from influenza since October, when the flu season began, said Ann Garvey, deputy state epidemiologist. Garvey could not say whether Ayzlee's death was included in the statistics.

The state does not receive reports of adult deaths caused by the flu, Garvey said.

However, Iowa Department of Public Health reports show that for the week ending Dec. 27, 161 Iowans were hospitalized with the flu at a set of hospitals the department monitors. More than half of the patients were 65 or older. The number of people hospitalized with the flu was up from 130 for the week that ended Dec. 20.

Nationally, the flu is now so widespread that the Centers for Disease Control and Prevention officially consider the outbreak an epidemic, but experts say it's impossible to predict its eventual severity.

In December, UnityPoint Health-Des Moines, which includes Iowa Methodist, Iowa Lutheran, Methodist West and Blank Children's medical centers, treated 360 patients who tested positive for the flu, a spokeswoman said. The centers had 22 people with the flu Jan. 1-2.

Mercy Medical Center in Des Moines admitted 116 people with the flu between Dec. 1 and 10 a.m. Dec. 31, a spokesman said.

"It's hard to predict how high the numbers of people who get the flu will climb or how long the season will continue," Garvey said.

The spike in flu cases has prompted Des Moines medical centers to tighten visitation guidelines. In general, hospital patients are allowed only two visitors at a time. People who show any flu symptoms are not allowed to visit patients. In addition, those who visit patients who have the flu must wear masks.

Adding to concerns: This year's version of the flu vaccine offers spottier protection than usual. Nationally, experts say that about half of the H3N2 strain of flu viruses has shifted its genes in a way that is not perfectly targeted by the vaccine.

Still, people who haven't gotten a flu shot this season are encouraged to do so. So far, about 650,000 doses of the flu vaccine have been administered to Iowans, similar to amounts in previous years, state health officials said.

"If people would get a flu shot, it can limit the severity of the flu symptoms if they get it," said Nola Aigner, spokeswoman for the Polk County Health Department. "The shot offers protection for the other strains. ... This is a serious illness, and it can affect healthy people."

Ayzlee McCarthy, who turned 3 on Dec. 16, was a healthy — and very active — child, her mother said.

The girl, who lived in Elk Horn with her parents, sister and brother, spent Christmas opening presents and running around, her mother said. On Dec. 26, Ayzlee played with her new toys, particularly Olaf, a snowman doll from the movie "Frozen."

When Ayzlee woke up on Dec. 27, she complained that her legs ached so badly that she couldn't walk. She ran a fever but didn't show any other signs of having the flu, said her mother, who is a respiratory therapist. Amber McCarthy said she thought her daughter might have a urinary tract infection, and took her to a clinic, where she tested positive for the flu.

"She tested positive for both A and B" types of influenza, Amber McCarthy said. "I never in a million years thought that was what we'd be at the clinic for."

Amber McCarthy took her daughter home and followed medical professionals' instructions: She made sure Ayzlee drank plenty of fluids and gave her ibuprofen and other medicines.

Ayzlee's fever broke later on Dec. 27, and her mother said she thought her daughter was feeling better. They watched cartoons together while Jim McCarthy took the couple's two other children to a family Christmas gathering.

"I made her some toast, and she told me what a good 'cooker' I was," Amber McCarthy said.

On Dec. 28, Ayzlee seemed to be better and didn't complain about feeling ill, her mother said.

By later in the day, though, Amber McCarthy said her daughter seemed to be getting worse. "She sat there looking through me and not at me," she said. "I knew something was not right."

Amber McCarthy took Ayzlee to the hospital in nearby Atlantic, where the staff did bloodwork and hooked the girl to an IV. A few times, Ayzlee didn't recognize her mother.

"After she was hooked up to the IV, she started perking up and getting feisty," Amber McCarthy said. "She tried to take her IV out, stuff like that."

Amber McCarthy was told Ayzlee could stay in the Atlantic hospital or be transported to Blank Children's Hospital in Des Moines. She opted to send her daughter to the Des Moines center. The two rode in a transport vehicle together — Ayzlee in the back watching the movie "Frozen"; her mother in the front.

At Blank, Ayzlee's condition worsened, her mother said. The girl's oxygen levels dropped, and her breathing became labored.

"She kept saying how tired she was," Amber McCarthy said.

She spent the night with her daughter, lying with her in her hospital bed.

At about 4 a.m. Dec. 29, Amber McCarthy woke up and looked at her daughter, whose breathing was once again labored and whose heart was racing. She called for a nurse, and said she remembers Ayzlee saying to her, "Mommy, I so tired. I done."

"I thought she was tired of (the hospital staff) picking on her," Amber McCarthy said.

The staff wanted to intubate Ayzlee, so her mother hugged her daughter and told her that she loved her.

As she was waiting in the hallway for the procedure to be completed, Ayzlee's heart stopped beating.

Doctors tried to revive her.

"They tried three times to bring her back. I said, 'Keep doing it,' " said Amber McCarthy, whose husband was on his way to the hospital. "By the time Jim got (to the hospital), we were able to go in and talk to her while she still had a heart rate."

After Ayzlee died, the hospital staff wrapped her in a blanket and let the McCarthys hold their daughter.

Ayzlee's funeral was Thursday.

"This shouldn't be happening in 2015," Amber McCarthy said.

Flu facts

Here are facts about the flu from the Iowa Department of Public Health: