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Two U.S. research groups have reported finding nearly 300 cases of an alarming apparent side effect of Covid-19 in children, a condition called multisystem inflammation syndrome, or MIS-C. While researchers have previously reported on the condition, the papers mark the first attempt to measure how frequently the side effect occurs and how it affects children who develop it.

The studies, published in the New England Journal of Medicine, describe children who develop severe inflammation affecting multiple organ systems after having had Covid-19, sometimes between two and four weeks after the infection. The majority of the children were previously healthy.

In one of the studies, led by researchers at Boston Children’s Hospital, 80% of the children who developed the condition required intensive care, 20% required mechanical ventilation, and four children, or 2%, died. In the second study, from researchers from New York state, a similar percentage of 99 children who developed the syndrome required ICU care and two children died. In both studies, many of the children developed cardiovascular and clotting problems and many had gastrointestinal symptoms. A high proportion also had skin rashes.


“Ours were really sick kids,” said Adrienne Randolph, an ICU physician at Boston Children’s Hospital and senior author on one of the papers, which was based on reports from 26 states.

Manish Patel, from the Centers for Disease Control and Prevention’s Covid-19 response team, said the message to parents is they should be on the lookout for fever and rash in children who have recently had Covid-19.


“I think being a little vigilant is important,” said Patel, who is an author on Randolph’s paper. “Fever, rash and I think especially in the setting of areas where you have a lot of coronavirus infections, SARS-CoV-2 infections — have a lower threshold for seeking care, I would say.”

On the whole, children appear to contract SARS-CoV-2 less often than adults and have a milder course of disease when they do.

But in late April, doctors in London alerted the world to the possibility that some children who had Covid-19 appeared to go on to develop something that looked like Kawasaki’s disease, an inflammatory condition that can attack the heart. KD, as it is called, is generally seen in children under the age of 5. Shortly thereafter, doctors in New York began to report cases as well.

In mid-May, the CDC asked doctors across the country to be on the lookout for cases of multisystem inflammatory syndrome in children.

The nearly 300 cases identified in these two studies share some similarities with KD, but there are also differences. Few of the children are under the age of 5. The average age of children in the larger study was 8; 42% of the children in the New York cohort were aged 6 to 12.

Another difference: While KD disproportionately affects children of Asian descent, MIS-C cases in the New York cohort were of all racial and ethnic backgrounds, the researchers reported.

“Among our patients, predominantly from the New York Metropolitan Region, 40% were Black and 36% were Hispanic. This may be a reflection of the well-documented elevated incidence of SARS CoV-2 infection among black and Hispanic communities,” they wrote.

The New York group estimated that the majority of MIS-C cases occurred about one month after the peak of Covid-19 cases in the state. They estimated that between March 1 and May 10, two of every 100,000 people under the 21 years of age who had laboratory-confirmed SARS-CoV-2 virus developed MIS-C in the state. The infection rate in people under the age of 21 years was 322 in 100,000 over that period.

An editorial written by Michael Levin, from the department of infectious diseases at Imperial College London, said there have been roughly 1,000 pediatric cases of the condition reported worldwide to date. He suggested more are likely going unrecorded, because case definitions require evidence of prior Covid-19 infection.

“There is concern that children meeting current diagnostic criteria for MIS-C are the ‘tip of the iceberg,’ and a bigger problem may be lurking below the waterline,” Levin wrote.

This article was updated to include information from the New York state study.

  • The following quote cannot be correct, “They estimated that between March 1 and May 10, two of every 100,000 people under the 21 years of age who had laboratory-confirmed SARS-CoV-2 virus developed MIS-C in the state.” This would mean there were 5 million confirmed cases in under 21 year old’s in New York to have 100 cases of MIS-C. In fact, the article states that the overall incidence rate was 2 per 100,000 total individuals under 21, not 2 per 100,000 SARS-CoV2 infected individuals under 21. This represents 0.6%, or 6 cases of MIS-C per 1,000 cases of lab confirmed SARS-CoV2 infection in this age group.

  • I really don’t care for these post hoc retrospective case study analyses.

    Not because the doctors/scientists aren’t trying to do something useful, it’s that just the fear mongering press, including STAT, take these studies and breathlessly trumpet their results. Do they ever closely READ the detailed “study limitations” paragraph that all these papers have? If they do, their articles don’t address those limitations.

    Moreover, the STAT journos never talk to anyone who might see the potential flaws in this study. Contrary opinions from equally prestigious sources? Fuggedaboutit.

    So, here we go.

    NEJM study looks at — ahem — the “temporal association” of the virus and this syndrome. Nicely chosen words there. And 186 patients during the pandemic out of….what…how many children who get MIS-C WITHOUT the Wuhan? What is THAT number? That number is nowhere to be found.

    Meanwhile of the 186 patients in the NEJM article, 137 were deemed “healthy.” OK, what does that mean, exactly? Did they come to that conclusion based on their detailed pediatric records, assuming those patients had them? Were any of the 137 obese? Maybe some of them get wheeled in with undiagnosed sickle cell anemia or asthma? Or were their health records specific about these patients NOT having co-morbidities? Or was it just a fast workup by a stressed out HCP.

    And what about the remaining 51 who, by inference, were NOT healthy? What were their co-morbidities? How many were Type 1 diabetics? How many had cerebral palsy?

    And what about the the 2 patients who died? Were they from the healthy pool, or the non-healthy pool? And if from the non-healthy pool, what were their co-morbidities?


    Here’s what articles like this do. Scare the pants off of normal parents, with normal children who, because of such panicky reporting, keep their kids out of school and away from socializing with other people with all the resultant NEGATIVE benefits such choices entail.

    • At present, a lot of decisionmaking on many levels is being done regarding re-opening schools in the fall. The article’s timing has “temporal association” with public opinion being formed on this subject.

  • These bits of the virus that show up on testing after recovery, could this make it easier to form a new virus? (a mixture of two or more). Pardon my ignorance on the subject.

  • So IMO we should be seeing data on IL6 blockers when given sooner rather than later.
    Is this not a type of cytokine storm?
    Correct me if I’m wrong

  • A doctor friend of are is MD suburb said her email group saw an unexpected Kawasaki’s-symptomology uptick as early as by late November, 2019. There could be more cases out there than currently identified.

  • This is just another endothelial disease like KD or HUS, this time caused by COVID.

  • The numbers don’t add up.
    If MIS-C only occurs in 2 per 100,000 infections under 21 and the rate of infection is that age group is 322 per 100,000 then simple math reveals that 322,000 infections would occur in 100,000,000 under 21 years and thus there would be 6.44 cases od MIS-C in a population of under 21 yrs numbering 100,000,000.
    To reach the 300 cases described using these stats then there would have to have a pool of under 21 year youths of 5,000,000,000 which is more than the total of under 21 year olds in the entire world.

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