Most kids with inflammatory COVID-19 syndrome are recovered by 6 months

A child in a hospital bed.
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Many children who develop a rare inflammatory syndrome after COVID-19 see their most serious symptoms clear up by six months, a new study suggests.

Although the study was small, involving fewer than 50 kids with the condition, called multisystem inflammatory syndrome in children (MIS-C), the authors say the results are encouraging.

"These findings can hopefully signal cautious optimism that many of the most severe effects of [MIS-C] appear to resolve within six months," study co-author Dr. Justin Penner, of the Department of Pediatric Infectious Diseases at Great Ormond Street Hospital in London, said in a statement. Still, some children did experience persistent fatigue and difficulty exercising that should be closely monitored, the researchers said.

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MIS-C was first discovered in April 2020, and involves inflammation of multiple organs, such as the heart, lungs, kidneys, brain, skin, eyes and gastrointestinal tract, according to the Centers for Disease Control and Prevention (CDC). Kids with the condition may experience fever, rash, abdominal pain, vomiting or diarrhea, usually after testing positive for COVID-19, and they usually need to be hospitalized. The condition is rare — after about 1 year, a total of 3,742 cases of MIS-C and 35 deaths have been reported in the U.S., according to the CDC; while about 4 million children have tested positive for COVID-19 since the beginning of the pandemic, according to the American Academy of Pediatrics.

The new study, published Monday (May 24) in the journal The Lancet Child & Adolescent Health, is the longest study of MIS-C to date, following children for six months after their hospitalization. The researchers analyzed information from 46 children who were hospitalized with MIS-C at Great Ormond Street Hospital from April to September 2020.

At the time they were hospitalized, all of the children had body-wide inflammation, meaning they had increased levels of inflammatory markers in their blood. The vast majority, 98%, had gastrointestinal symptoms, 52% had neurological symptoms and 33% had heart symptoms.

However at six months, just one child (2%) still had systemic inflammation, two (4%) had heart abnormalities and six (13%) had gastrointestinal symptoms. None of the children died.

What's more, 98% of the patients had returned to school full time (virtual or in-person). 

And scores on a test of muscle strength improved from 53 out of 80 (with higher scores indicating better strength) during hospitalization to 80 out of 80 at 6 months.

About 40% of patients showed subtle abnormalities on specific neurological tests, such as slight problems on tests of coordination, reflexes and eye movement. But these abnormalities didn't translate into "functional impairment," that is, the children didn't have problems with their ability to perform everyday tasks, such as walking, the authors said.

Still, some had trouble exercising, as measured by a test of how far they could walk in 6 minutes. Six months after hospitalization, about 40% of the children scored in the bottom 3% for their age and sex on the walking test. 

But this finding is difficult to interpret because the study did not compare to the walking speed of children who were not hospitalized with MIS-C, the authors said. It's possible that during the pandemic, even healthy children experienced reductions in their exercise ability, given that lockdowns prevent people from exercising normally.

"The levels of fatigue and muscle weakness we found at six months follow-up are concerning and requires close monitoring, but it's difficult to determine whether this finding is caused directly by [MIS-C] or if it's a result of the disruption in children’s lives that the COVID-19 pandemic has caused on a wider scale," study co-author Dr. Karyn Moshal, of Great Ormond Street Hospital's Department of Pediatric Infectious Diseases, said in a statement. 

The new study also cannot rule out the possibility that additional long-term effects might show up in the children more than six months after hospitalization (such as kidney disease, which sometimes appears more than six months after a severe illness), and so it is important to continue follow-up studies on MIS-C patients, the authors said.

Originally published on Live Science.  

Rachael Rettner

Rachael is a Live Science contributor, and was a former channel editor and senior writer for Live Science between 2010 and 2022. She has a master's degree in journalism from New York University's Science, Health and Environmental Reporting Program. She also holds a B.S. in molecular biology and an M.S. in biology from the University of California, San Diego. Her work has appeared in Scienceline, The Washington Post and Scientific American.