Why is the flu killing so many American children?

Hundreds of young people have died from the virus over the last several years as doctors attempt to predict the best vaccines to combat the annual outbreak

Ohio teenager Kaylee Roberts died on New Year's Eve, a week after feeling sick with the flu. (Matthew Roberts)

Kaylee Roberts had just earned her learner's permit. She was 16 years old and excited about getting behind the wheel.

While on winter break from high school in suburban Cleveland, she came down with what she thought was a bad cold just as her family was preparing to spend the Christmas holiday together.

Doctors told her she had a case of flu. A week after opening presents at her aunt's house on Christmas Eve, Kaylee died on New Year's Eve.

"She was a really bright, intelligent, beautiful young girl", her uncle Matthew Roberts tells The Independent. "She was such a wonderful person, a very good big sister ... She meant the world to her mother and father."

After falling within the first two weeks of 2020, rates of flu activity are once again on the rise, with climbing hospitalisation rates and nearly every state in the US reporting high rates of illness.

But the 2019-2020 flu season has been marked by a tragic streak of deaths among people under age 18. This season, 78 children have died from the flu and complications from the virus, as of this writing.

Health officials warn that despite the media coverage and international health emergency posed by the emergence of coronavirus, flu remains a constant and predictable health crisis.

Hundreds of people have died in China following a coronavirus outbreak that surfaced last month. The virus has infected thousands of people in more than a dozen countries, and the US has blocked travel and mandated quarantines for people entering the country from the viral epicentre in China.

As of this writing, the Centers for Disease Control and Prevention reports that 12 people contracted coronavirus in the US.

However, as many as 26 million people in the US had or are expected to get the flu this season. Flu viruses and complications from influenza have claimed as many as 10,000 lives.

Dr Anthony Fauci with the National Institutes of Health said there's a near-certainty of what to expect from a seasonal flu with a "guarantee" that the rates will go down in the spring. What makes coronavirus more dangerous, he says, "is there's a lot of unknowns" with the mysterious illness as the number of cases continue to climb.

'This virus did not read the textbook'

Kaylee loved singing in her school choir, watching movies with her dad, and "doing all the things teenage girls love doing", Matthew Roberts says.

"She was the chosen one", he says. "Beautiful, intelligent, humble, down to earth, caring."

On 21 December, Kaylee was starting to feel a cold coming on.

On Christmas Eve, she was achy, with a fever, coughing and vomiting. The family took her back to a hospital emergency room, where she spent several hours. She was dehydrated so doctors gave her potassium and fluids. Her chest X-rays were clear, though she had a wet cough. Doctors confirmed: She had the flu.

Doctors prescribed her Tamiflu, an antiviral medication, and told her to go home, rest and rehydrate.

On the way home, the family stopped at her aunt's house. She coughed into a face mask as she opened presents.

On Friday morning, her breathing had changed. Doctors put her in an ambulance to Rainbow Babies and Children's Hospital in Cleveland. Now she had pneumonia. Chest X-rays showed that her entire left lung and most of her right lung "were being attacked" and were filling with fluid, Mr Roberts says.

Early on Sunday morning, her oxygen levels dropped dangerously low. Doctors incubated her to help her body keep breathing.

An unusual and terrifying rash of aggressive complications began to form -- blood clots, a stroke, liver and kidney failure.

On Tuesday morning, doctors said there was nothing more they could do.

Kaylee is among dozens of young people in the US whose rapid illness and hospitalisation sprung from a strain of flu that has vexed doctors and underlined the importance of getting an annual flu shot.

Less than 72 hours after she complained that she was feeling ill with body aches, North Carolina teenager Lacie Rian Fisher was unconscious, falling limp into her family's arms. She decided to skip cheerleading practice on Friday and was pronounced dead on Monday morning.

In Atlanta, Georgia, 17-year-old John Chelcy was hospitalised for several weeks after experiencing excruciating pain, then placed into a medically induced coma with kidney failure.

Both teens had contracted influenza B virus, just like Kaylee. None of them received a flu vaccine this season.

The CDC reported 186 flu-related deaths among children during the 2017-2018 season, and 116 children died during the 2018-2019 season.

During the deadly 2009 flu pandemic, the CDC reported 358 paediatric deaths.

Dr William Schaffner, professor of preventive medicine at Vanderbilt and an advisor with the CDC, warns against trying to predict a flu season and how it impacts people: "If you've seen one flu season, you've seen one flu season."

Young, strong immune systems often are considered the best defence against viruses like the flu. But those same healthy bodies also can over-correct as they combat illness, creating a "paradoxical effect" that forgets to tell an immune system "to keep the foot off the gas pedal", he says.

Children can be resilient against the flu, he says, but children with underlying illnesses or whose immune systems have been compromised are "more predisposed to a severe outcome", he says. "Trap, kill, so we can recover -- standard operating procedure for our system."

But the opposite is often possible, with lethal flu cases appearing in children who are otherwise normal and healthy before their infection.

"It's at the core of why we recommend children be vaccinated", he says. "You can't pick out those who overreact."

This year's flu came on "early and aggressively" with an unusual outbreak of an influenza B/Victoria strain. That strain typically will "smoulder around in the background" and become more prominent at the end of a flu season, he says.

Of the 78 reported flu-related paediatric deaths during the 2019-2020 season, 52 were associated with B viruses, while 26 deaths were associated with influenza A viruses.

"Nobody really knows" why a particularly aggressive strain dominates the flu cycle in its early stages, Dr Schaffner says. "This virus did not read the textbook."

'They're not perfect vaccines'

More than 173 million doses of flu vaccine have been distributed this flu season.

Dr Schaffner dispels the myth that a flu vaccine will cause a person to get the flu: "There's absolutely no substance to that whatsoever."

Because flu strains mutate over time, vaccines must be able to anticipate the season's dominant strains months ahead of their outbreak. When the vaccine is off-target, it's likely because the virus has mutated, Dr Schaffner says.

"We recognise they're not perfect vaccines", he says. "[But] if you get the vaccine and nonetheless get influenza, you will have a less severe case. ... We give the vaccine to prevent the disease, but also to moderate it, to shift the odds in our favour that we will do well."

Vaccinated people also are less likely to give the virus to someone else.

Dr Schaffner warns Americans to avoid people coughing and sneezing, use "good hand hygiene", and if you need to see a doctor, call a health provider first before potentially exposing the virus to people in a waiting room. Doctors may be able to prescribe antiviral medication to reduce the spread of illness.

Mr Roberts says: "From a family perspective, we definitely want to get the message out, that if your child has any signs of flu, respiratory illnesses, take them to the doctor, and have all the questions asked and all the bases covered."