Just about half of eligible Americans get their flu shots.

For many of us, the flu is a temporary annoyance that can leave us aching, feverish, and confined to bed. But for thousands of people in the United States, it can be deadly.

Serese Marotta, the chief operating officer of Families Fighting Flu, works with families who have seen their children injured, hospitalized, or even fatally infected after contracting the flu.

The charity was founded in 2004 with the ongoing mission to increase awareness and educate the public about the importance of influenza vaccination. The charity is “dedicated to protecting children, families, and communities against the flu.”

“I can tell you a hundred different ways that healthy children have died from flu and no two of them are exactly the same,” she said. “That’s what’s so scary about influenza. It’s unpredictable.”

This year’s flu season has been among the worst in a decade with infection rates rising. Today the U.S. Centers of Disease Control and Prevention (CDC) said that the seasonal flu has left 63 children dead.

Marotta said that getting vaccinated every year against the flu isn’t just important for people as individuals, but to bolster “herd immunity.” This means getting vaccinated to protect others whose immune system isn’t as strong. In addition to elderly people, young children and pregnant women are more susceptible to complications from a flu infection.

“So often, we hear, ‘Oh, I’m strong, I’ve never had the flu. I don’t need the flu shot.’ It’s not just about protecting yourself,” she said. “People don’t realize that it’s a public health issue.”

Marotta knows firsthand how devastating a flu infection can be. In 2009, her son died after contracting the H1N1 influenza, during the swine flu pandemic.

“If you had asked me before Joseph passed away, ‘What is the biggest threat to your children?’ Flu would not have made my top 10 list,” Marotta told Healthline. “I had no idea how serious it could be.”

In October 2009, Serese and Joe Marotta were raising their 7-year-old daughter, Emma, and 5-year-old son, Joseph, in Dayton, Ohio. The whole family had been vaccinated for seasonal influenza in September.

But the swine flu was different. Originating from North America, it was a new flu strain that led to a global pandemic. It arrived in 2009 and spread quickly, leaving little time for experts to develop and release a vaccine to protect people.

The first sign something was wrong was when Joseph was sent home from kindergarten and appeared to be lethargic.

A local urgent care found his blood oxygen to be low, and he was admitted to the children’s hospital, where he was diagnosed with pneumonia. Initial flu tests came up negative.

Over the next week, Joseph was treated for pneumonia and was also diagnosed with the new swine flu strain. Although Joseph was hospitalized, Marotta said she didn’t feel that the situation was dire.

After one week in the hospital, Joseph made it out of bed on a Saturday morning.

“We were trying to get him to eat pancakes,” Marotta said. “He was talking, giving me his usual stubborn thing, his usual sassy self. I was like, ‘We’re in a good place, and we’re doing what we need to do so we can get out of here and go home.’”

But Joseph was complaining of stomach pain and his health started to decline suddenly. He died one day later.

The Marotta family authorized an autopsy to understand how a flu could have led to his death.

“The H1N1 flu virus had actually gotten into his intestinal tract, and eroded it away from the inside out,” Marotta said.

She had questions. “What did we miss? It wasn’t accusatory. It was: What can we learn from this?” she explained. “My son just died from influenza. I had never heard of this happening before.”

But the flu can cause unexpected complications.

“So often we hear, ‘Flu is a respiratory disease,’ and yes, it is, but we also have to understand that it’s the complications of flu that can affect all those other target organs in our body and cause death,” she said.

After Joseph died, Marotta thought, “I can’t be the only one who lost a child to flu.” So, she went online, looking for families who had had similar experiences.

Among the responses to the local media’s coverage of Joseph’s death, Marotta noticed a comment from the then-executive director of Families Fighting Flu.

“I was like, ‘What is this Families Fighting Flu?’ I couldn’t get on the phone fast enough,” she recalled. “I said, ‘Oh my God, there are all these other families.’ I knew I wanted to make something positive out of this tragedy that we had suffered.”

While Marotta’s family didn’t have the chance to get the swine flu vaccine before Joseph’s infection, she has made it her life’s work to raise awareness of the importance of influenza vaccination for those who do have that chance.

“There are people in this organization who have lost children, whose children were not vaccinated,” she said, “and they will forever live with the what if question.”

Flu vaccination isn’t perfect, but it is the best way to protect against a dangerous influenza infection.

Today the H1N1 flu strain continues to circulate, along with other influenza strains during seasonal flu outbreaks. This year the seasonal flu vaccine was designed to provide protection against H1N1.

Even a less effective flu vaccine can save thousands of lives every year. While it may not stop a flu infection, it can lessen the severe symptoms.

One study from the CDC found that the vaccine saved 40,000 lives over a 9-year period.

But in the United States, just about half the population currently receives the vaccine for influenza.

Dr. William Schaffner, professor of preventive medicine and infectious diseases at Vanderbilt University, told Healthline: “We give something on the order of 150 million doses, plus or minus, of flu vaccine each year. We’re almost halfway to where we ought to be.”

This is just not enough.

“Half of our fellow Americans do not receive the vaccine,” he said. “And we wish they would for their own benefit. It would also make our community safer, because when you get the vaccine, of course, you’re much less likely to pass that virus on to anyone else. Nobody wants to become a dreaded spreader.”

But with spring around the corner, is it too late to get the flu vaccine?

“No! But it is late,” Schaffner said. “Get it this afternoon! Stop thinking about it. Make a belated new year’s resolution. When it comes September, October, this fall, in 2018, be the first in line, and bring everyone in your family with you, in order to get your influenza vaccine.”