CNN
 — 

Jessica Richman felt fear rush over her – again.

In October, she watched her 3-year-old daughter, Layla, become unusually lethargic, develop a high fever and start to have shortness of breath. It was a painful reminder of her other daughter, Cayden, who died of the flu in December 2014.

Cayden had been the same age as Layla.

“It was very similar symptoms to Cayden. So, of course, I jumped into high gear,” Richman said.

When Layla’s symptoms began on Halloween, Richman took her to an urgent care clinic in their hometown of Newport News, Virginia.

“Her heart rate was elevated. Her fever was very high. They kept her there for most of the afternoon to observe her,” Richman said. “I explained to the doctor that was there that I have lost a 3-year-old daughter to the flu, so this was very scary for me. He really took that to heart.”

Layla’s medical team diagnosed her with influenza and gave her Motrin for her fever and the antiviral Tamiflu to treat the infection.

“She felt better fairly quickly, within 24 hours,” Richman said.

Richman’s experience during this flu season was dramatically different than in 2014, when she lost her beloved Cayden.

One key difference: Cayden was unvaccinated in 2014. Layla got her vaccine in September.

“I really think that the vaccine played a big role,” said Richman, who serves as secretary for the nonprofit Families Fighting Flu.

Even though Layla became sick when she encountered the flu virus weeks after vaccination, “she recovered quickly,” Richman said, adding that no one else in their household – which also includes her husband, Matt, and their 6-year-old son, Parker – caught the flu from Layla.

All of them had been vaccinated before Layla’s illness.

The US Centers for Disease Control and Prevention estimates that at least 16,000 people have died of flu this season, and at least 79 deaths have been in children.

Seasonal flu activity continues to be very prevalent across the United States but has been declining in most areas in recent weeks. Still, public health officials encourage people to get their annual flu vaccine as the best way to protect against that virus.

Many people who don’t get their seasonal flu shot are not necessarily anti-vaccination. They simply might not have had the time. That was the case for Cayden in 2014.

That year, Richman and Cayden’s father got their flu shots, but Cayden’s vaccination had to be rescheduled because she had a cold at the time.

“Because I also at the time was ill-informed about the flu, I didn’t feel that it was super urgent to go and immediately get her flu shot as soon as she was well,” Richman said. “I kind of put it off.”

One Thursday some weeks later, Cayden wasn’t her usual talkative and bubbly self. The 3-year-old, affectionately known as CadyBug, was fatigued and developed a cough. She stayed home from daycare with her father, and he took her to the pediatrician’s office.

The doctor thought Cayden’s symptoms were probably from a cold virus and sent her home without testing for the flu, Richman said.

The next morning, Cayden still had a fever. She was coughing and kept asking for water. Her father took her back to the pediatrician’s office but was sent home again.

“No one tested her for the flu. No one seemed to think that this was flu,” Richman said. “She was sent home that Friday afternoon.”

When they got home, Cayden’s symptoms worsened.

“She deteriorated very, very fast. It was in a matter of hours,” Richman said. “It was very deep, shallow breaths. She was not breathing correctly.”

Richman said that she was driving home from work when she got a chilling phone call from Cayden’s father: Cayden had stopped breathing during her nap. He had called 911. Richman arrived home to find emergency vehicles in front of her house and paramedics working on Cayden.

“She could not be resuscitated at the house,” Richman said. “In the ambulance ride, they had not told me at the time that she could not be resuscitated, but I could tell because I was riding in an ambulance and there was no noise. So I knew that it was over.”

When Cayden died, her parents still had no idea that it was because of the flu.

“It wasn’t until we received an autopsy that I clearly understood that it was the flu that caused her lungs to fill with mucus until she could no longer breathe,” Richman said. “I had no idea what happened until we got the autopsy back.”

Before Cayden’s tragic death, her mother was unaware that the flu could turn fatal.

“I was completely taken aback,” she said. “I had no idea that that could ever happen.”

Nearly a decade later, Richman and her family get their flu shots together each year in remembrance of Cayden. They wear pink and share social media posts about it, using the hashtag #pinkforcadybug, since pink was Cayden’s favorite color.

The most common symptoms of flu are fever, body ache and shaking chills. In some cases, it can cause lower respiratory tract infections known as pneumonia or directly infect heart cells and brain cells, causing inflammation of those organs, Dr. Tara Vijayan, an infectious disease doctor at the David Geffen School of Medicine at the University of California, Los Angeles, said in an email.

She added that inflammation can result in the body’s own cells dying.

“More commonly, however, if the flu is going to cause severe disease it is because it disrupts the lining of the respiratory tract such that the lungs become more susceptible to other bacterial pneumonias,” Vijayan said. “Generally, those who are unvaccinated and have multiple medical problems or have lowered immune systems are at highest risk, but we have seen death in younger otherwise healthy people.”

She added that people older in age or who are pregnant are also at high risk of complications.

Treating patients with severe flu is a frequent but difficult experience for Dr. Ali Khan, who specializes in internal medicine at one of the primary care network Oak Street Health’s Chicago locations.

“It is an incredibly difficult infection to watch as a clinician,” Khan said, adding that flu infections can turn deadly when someone gets a superimposed bacterial infection like pneumonia or develops severe sepsis.

“We get folks who are coming in to hospitals with seizures or with encephalitis caused by the flu. Folks who are coming in with significant muscle injury and breakdown, like the kind that you get when you’re quite dehydrated and overly fatigued,” he said. “Suffice to say, I’ve seen this far too many times than I’d ever like to see as a clinician.”

It’s not too late to get this season’s flu shot if you haven’t done so, Khan said.

“We’re not out of the woods yet,” he said. “Absolutely, you can still get vaccinated.”

Vijayan had similar sentiments.

“Our flu rates were unexpectedly high in the late fall and it does seem to be leveling off, but I would absolutely be concerned about another rise in cases this winter,” she said. “It is absolutely not too late to get the flu shot.”