Tammie Hairston knew something was wrong.
In early May, her son Kyree McBride, 9, developed a fever that lasted for several days.
A trip to the emergency room at Children’s National Hospital in Washington, DC, and to her son’s primary care physician revealed nothing.
But when Kyree developed redness in his eye, she knew it was time for another trip to the hospital.
“Normally, I don’t worry, because my son is not a sickly kid,” Ms Hairston said.
“We’re never in the hospital, maybe for bumps and bruises but never because he is sick. But I was worried.”
Doctors tested Kyree for Covid-19. The results came back negative, but he was still feeling under the weather. They decided to run an antibody test.
The results showed that at some point, Kyree had contracted Covid-19 but he had never showed any symptoms.
With that, doctors at Children’s National Hospital, which is home to the Sheikh Zayed Campus for Advanced Pediatric Medicine, were able to deduce that he had an exceedingly rare reaction to the virus known as Multi-system Inflammatory Syndrome in Children, or MIS-C.
To date, there have only been 2,617 documented cases of children with MIS-C in the US.
But by far most of those cases occurred during the second wave of the pandemic.
Doctors are not sure why there has been a surge in cases in recent months.
At the Children's National Hospital, doctors have treated 150 children suffering from MIS-C.
The syndrome is characterised by inflamed organs and can have serious and even fatal effects on children.
“They can have decreased squeeze of the heart muscle, or shock, where you need medicine to support your blood pressure and help get oxygen to your body,” said Dr Anita Krishnan, a paediatric cardiologist at the Children's National Hospital.
“The sickest kids might even go on ECMO [extracorporeal membrane oxygenation], which is the life support machine and can get inflammation in their coronary arteries, which are blood vessels that feed blood to your heart.
"They can become dilated or get aneurysms in them.”
For Kyree, MIS-C meant spending five nerve-racking days at the hospital as doctors ran test after test and searched for ways to help him improve.
Like many children with MIS-C, tests showed that his heart was enlarged.
“He did pretty well throughout the whole thing,” said his mother. “But when he saw me worry, he became more afraid.
"He said: ‘Mummy, I’m sorry I put you through this’, and I was like: ‘Oh no, don’t ever be sorry about this. This is what Mummy is supposed to do.'"
Ms Hairston agreed to enrol Kyree in a nationwide study on the long-term effects of MIS-C on children, called Music.
The Covid Music study was launched in September 2020.
The research, led by the National Institute of Health, hopes to enrol about 600 children from the US and Canada and include the participation of 29 children’s hospitals to better understand how the disease affects children.
Dr Krishnan, who is contributing to the study, said she was concerned about the possible long-term effects on children.
"Initially, I may have thought their heart is better so now we're out of the woods," she told The National.
“But we’re starting to see some signs that kids may have some symptoms for a longer time, like changes in their mood or more chronic symptoms.”
Ms Hairston said she enrolled Kyree in the study to help other mothers and children.
“That’s why I agreed to be in the study, because they’re still learning and if my kid can help another kid, it’s all about educating," she said.
In the months since Kyree was discharged, he has continued to see a cardiologist periodically but has mostly returned to normal.
“He’s OK, he’s back to my normal kid,” Ms Hairston said.
But she said that recently Kyree had complained of chest pains again.
After what they went through in May, she is not taking any chances.
She has scheduled another appointment with the cardiologist, first thing next week.