More than half of U.S. adults have now received at least one COVID-19 vaccine, but children remain unimmunized and unprotected from potential infection.

The American Academy of Pediatrics is now reporting that in some states, up to 18% of all COVID-19 cases occurred in children during the month of April. In Michigan, where COVID-19 cases have surged in recent weeks, there has been a 237% increase in admissions to pediatric hospitals from mid-February to mid-April.

While children overall tend to only have mild symptoms with SARS-COV-2 infection, as a higher percent of children contract the virus, some will likely experience severe respiratory disease.

It is also more likely that some will experience a rare consequence of infection with the virus, multi-system inflammatory syndrome, or MIS-C.

What is MIS-C?

The main features of this mysterious illness are persistent fevers and impaired functioning of many vital organs, including a serious heart condition known as cardiogenic shock.

The U.S. Centers for Disease Control and Prevention has recorded over 3,185 official cases of MIS-C in the U.S. since May 2020. Of those, 36 cases resulted in the death of a child.

Last year, in the early days of the pandemic, pediatric doctors in London set out to discover what sufferers of this disorder had in common.

None of the children's parents had been aware of any recent illnesses. Yet, each child's blood work was positive for high antibody levels against SARS-COV-2, proving recent infection with the virus. Like most young people, these children had all experienced a symptom-free infection.

What was going on?

It seems that for a very small number of children, after SARS-COV-2 infection, the immune system gets triggered inappropriately into producing massive amounts of unnecessary inflammation within the body.

This inflammation is what had caused the high fevers and dysfunction of the heart and other organ systems.

The pediatric doctors in London reported their findings on the first eight patients in April 2020. Children's hospitals worldwide started recognizing and reporting cases shortly afterward.

What can be done to protect children?

Though at first a medical mystery, one year later, doctors have now learned more about MIS-C, and how to treat it.

Researchers are actively investigating why the immune system is triggered so inappropriately after SARS-COV-2 infection in some children but not in others.

But for now, doctors have discovered the most effective way to treat MIS-C is to dampen down the over-exaggerated inflammation response in the body before permanent damage occurs.

Steroid therapy and intravenous immunoglobulin (a blood product made up of antibodies) reduce inflammation in the body. They are now proven to be successful first-line therapies for most children suffering from MIS-C. Some children will require admission to a pediatric intensive care unit for advanced medical support.

If a child does not respond to these first-line treatments, more targeted biological therapies to reduce inflammation are also available.

Experts say that MIS-C can be serious, even deadly, but that is extremely rare. Most children with MIS-C will have a complete recovery with appropriate medical care.

The symptoms of MIS-C can be highly variable. Some common symptoms include persistent fevers, abdominal pain, vomiting, diarrhea, neck pain, bloodshot eyes and fatigue.

Signs that a child should be seen immediately by a medical provider include the following; trouble breathing, persistent chest pain, difficulty staying awake, or pale blue-colored skin, lips, or nail beds, along with any other concerning signs.

Any parent concerned their child has MIS-C should contact their doctor immediately. Over the past year, doctors have learned how best to treat children with MIS-C, dramatically improving their chance of recovery.

Dr. Aine Cooke, MD, is a board-certified pediatrician.