Emily Lastinger, a wide-eyed toddler with a cherubic smile, had been sick with the flu for three days, but neither her parents nor her doctor were terribly worried.
"It was so weird: She would spike a fever and be really sick for a few hours, then she would bounce back and be hungry and want a Popsicle and run around a bit," said her father, Joe Lastinger, a 40-year-old health care executive from Colleyville, Texas.
But on Super Bowl Sunday in 2004, she began vomiting and her condition suddenly worsened.
"It was a really rough night," said Lastinger, who stayed up with the 3-year-old because his wife was pregnant, ready to deliver their fourth child.
On Monday morning, the toddler had a long shower and was sitting in bed watching cartoons. They had a doctor's appointment at noon.
"I was doing emails and I heard my wife start screaming upstairs," said Lastinger. "She had stopped breathing."
He started CPR and his wife called 911. Emily was rushed to the hospital and pumped with medicine in intensive care, but there was nothing more doctors could do. She had suffered brain damage and died that night.
"How could it possibly happen?" Lastinger and his wife asked themselves. "Honestly, you worry about your kid being struck by lightning at pool, you worry about car accidents or should they go on a trampoline or a car seat -- those kinds of things, but not the flu."
Both Lastinger and his wife had gotten flu shots that winter. But at 3, Emily fell outside the recommended age group -- then only children 6 months to 2 years old.
Two years later, the Centers for Disease Control (CDC) would broaden its guidelines to recommend vaccination for all children, not just those at risk, up to the age of 5.
"Emily was normal and healthy, and that's the thing," said Lastinger. "They weren't recommending vaccine for kids who were normal. ... Meanwhile healthy kids were sick and dying."
Today, thanks to efforts of parent support groups like the one Lastinger co-founded, Families Fighting Flu, the CDC recommends universal immunization from the age of 6 months.
In 2004, the CDC expanded vaccine guidelines up to age 59 months. In 2006, it was recommended through age 18. And in 2010, it voted for universal vaccination over the age of 6 months.
"We applauded it, though it came slowly from our perspective," said Lastinger. "We certainly feel like had they been in place, we would have followed them, our pediatrician would have followed them and our daughter would be alive today."
An estimated 100 otherwise healthy children die of the flu each year and about 20,000 under the age of 5 are hospitalized. Influenza kills anywhere between 3,000 and 49,000 adults annually, as well, according to the CDC.
"Children under 6 months of age have not been studied yet. Therefore, the flu vaccines are not licensed for use in that tender age group," said Dr. William Schaffner, chairman of the department of preventive medicine at Vanderbilt University School of Medicine.
"To protect them, we rely on mother's vaccination during pregnancy -- protection passes through the placenta into the baby -- as well as all contacts of the baby being vaccinated," Schaffner said.
Children under the age of 9 who get the flu shot for the first time need two immunizations in either a shot or nasal spray, to get maximum protection, "which puts a lot of responsibility on the parents," Schaffner said.
Getting just one shot is not enough, as the Moise family of Kansas City, Mo., learned.
Ian Moise died of complications from influenza A in 2003. The family's 7-month-old baby had only gotten the first of two recommended flu vaccine doses before it fell ill two weeks later.