ST. LOUIS, MISSOURI (REUTERS) - When her two-year-old started feeling sick early last week, Ms Tiffany Jackson did not think it might be Covid-19.

No one else in the family was sick. Adrian James just had a bit of a cough. She gave him cough syrup and put a humidifier in his room.

But by Friday (Oct 1) he was sweaty and his breathing was laboured.

Ms Jackson took him to an emergency room in her small town of Mount Vernon, Illinois. Doctors and nurses there did a chest X-ray and swabbed him for Covid-19 - and then airlifted the child to Cardinal Glennon Children's Hospital in St. Louis, about 129km away.

Ms Jackson followed in a car, her grandmother at the wheel. They made the usually 90 minute-drive in about an hour.

"I didn't know if he was going to make it or not," Ms Jackson said. "I was very emotional and just very upset."

Her son is one of more than 840,000 children under the age of four to contract Covid-19 in the United States since the beginning of the pandemic, according to the US Centres for Disease Control and Prevention (CDC).

Hospitalisations like Adrian's remain rare: less than 1 per cent of children with reported cases of Covid-19 are hospitalised and children account for 2.5 per cent of all Covid-19 related hospitalisations, according to the American Academy of Pediatrics.

While nationally Covid-19 cases and hospitalisations have fallen, parts of the US are being ravaged by the highly contagious Delta variant, which Adrian has.

By late Tuesday night, he was intubated and heavily sedated, wrapped in his baby blanket with his favourite Paw Patrol stuffed animal at hand.

Over the past couple of days, his lungs have been able to do more of the work of breathing, and it is possible that he may be removed from the ventilator soon.

The US last week crossed the milestone of 700,000 Covid-19 deaths since the pandemic started, including 520 children.

US health regulators will meet later this month to consider approving the Pfizer-BioNTech vaccine for ages five-11, followed later this year or early next year with a decision for those under the age of five.

Transmission of the virus remains high in every state except California and Connecticut, CDC data show.

'It is serious'

Adrian, who will be three years old next month, had developed pneumonia in his left lung. He was breathing fast, trying to gulp air with 76 respirations per minute, nearly twice the normal 40, Ms Jackson said.

At the hospital, doctors and nurses wearing masks, face shields and protective gowns sedated him and put him on a breathing tube attached to a ventilator in the intensive care unit.

Ms Jackson has been sleeping on a couch in his room in the ICU.

She does not know how her son contracted Covid-19. She had Covid-19 last summer. She says she did not get vaccinated for Covid-19 due to a rare auto-immune disorder called Guillain-Barre syndrome that she contracted as a result of a flu shot when she was 16.

The syndrome, which is incurable, causes nervous system damage.

Adrian's father, who is home with their younger child in Illinois, received one dose of a Covid-19 vaccine but not the second dose, she said.

Maybe, she thinks, someone at work passed it to him, although everyone in the factory where he is employed is supposed to wear masks and practice physical distancing.

Ms Jackson, 21, is profoundly grateful for the care her child has received. She is beginning to believe that it will save his life.

And she hopes that Adrian's story will help people understand what it could mean to pass the virus to young children and to people with vulnerable immune systems.

"I just want people to realise it is serious," she said.