MIS-C, or multisystem inflammatory syndrome in children, is a rare but serious condition in which a child’s immune system becomes severely overactivated weeks after a COVID-19 infection, causing widespread inflammation that can affect the heart, digestive system, skin, and other organs. It typically strikes 2 to 6 weeks after infection with SARS-CoV-2 and requires hospitalization, though most children recover fully within a few months.
How MIS-C Develops
MIS-C is not the COVID-19 infection itself. It’s a delayed immune reaction. After the virus has cleared, the immune system in some children essentially misfires and launches a massive inflammatory response against the body’s own tissues. One leading theory is that a part of the virus’s spike protein acts like a “superantigen,” a molecule that triggers an enormous, nonspecific immune response similar to what happens in toxic shock syndrome. This flood of inflammatory signals, sometimes called a cytokine storm, is what damages multiple organ systems at once.
Only a very small number of children who get COVID-19 go on to develop MIS-C, which suggests that genetic factors play a role. Certain children may carry gene variations that make their immune systems more prone to this kind of overreaction.
Who Is Most at Risk
MIS-C affects children and adolescents up to age 20, with a median age of 7 to 9 years. That’s notably older than Kawasaki disease, a similar inflammatory condition that primarily hits toddlers around age 3. The broader age range means MIS-C can appear in school-age children and teenagers who might otherwise seem past the window for these types of inflammatory syndromes.
Racial and ethnic disparities in MIS-C have been significant. CDC data shows that 31% of cases occurred in Black non-Hispanic children and 26% in Latino children. During the early months of the pandemic, the incidence of MIS-C was roughly 9 times higher in Black children and 9 times higher in Hispanic or Latino children compared to white children. Research has linked these disparities to a combination of genetic susceptibility, higher social vulnerability, and lower socioeconomic status, all of which were independently associated with developing MIS-C in a Massachusetts case-control study.
Symptoms to Recognize
MIS-C typically begins with a persistent fever, often after a child seemed to recover from a mild or even unnoticed COVID-19 infection weeks earlier. The hallmark of the condition is that it hits multiple body systems simultaneously. To meet the CDC’s diagnostic criteria, a child must have fever, require hospitalization, show elevated markers of inflammation in blood tests, and have new symptoms in at least two of the following categories:
- Heart: reduced pumping function, elevated markers of heart stress, or widening of the coronary arteries
- Skin and mucous membranes: rash, red or cracked lips, “strawberry tongue,” red eyes, or swelling of the hands and feet
- Gastrointestinal: abdominal pain, vomiting, or diarrhea
- Shock: dangerously low blood pressure requiring medical support
- Blood: low platelet counts or low lymphocyte counts
Gastrointestinal symptoms are especially common in MIS-C and can initially be mistaken for a stomach bug or appendicitis. Many children also experience neurological symptoms like confusion, headaches, or irritability, which helps distinguish MIS-C from other inflammatory conditions.
How It Differs From Kawasaki Disease
MIS-C shares visible features with Kawasaki disease, including fever, rash, red eyes, and the potential for coronary artery damage. But the two conditions differ in important ways. Kawasaki disease peaks in toddlers under 5, while MIS-C affects a wider age range centered around 7 to 9 years. Kawasaki disease requires at least 5 days of fever for diagnosis; MIS-C can be diagnosed after just 24 hours of fever.
The internal picture is also different. Children with MIS-C are far more likely to develop weakened heart pumping and signs of shock. Their blood work tends to show a distinctive pattern: low platelet counts (around 151,000 per microliter), whereas Kawasaki disease patients typically develop high platelet counts (above 365,000). Inflammation levels in MIS-C run much higher, with C-reactive protein levels averaging more than three times those seen in Kawasaki disease. Markers of heart stress are also dramatically elevated in MIS-C, sometimes by a factor of 10 or more compared to Kawasaki disease.
What Treatment Looks Like
Children with MIS-C are hospitalized, often in a pediatric intensive care unit. The primary goal of treatment is to calm the immune system’s overreaction and support the heart and other affected organs while inflammation subsides.
First-line treatment involves an infusion of concentrated antibodies (IVIG) combined with steroids to suppress the immune response. Most children respond to this combination. For children who are critically ill or don’t improve, doctors may escalate to higher-dose steroids or add a medication that blocks a specific inflammatory signal. Some children also need medications to support blood pressure if they’re in shock.
Because MIS-C can affect the heart and blood vessels, children may receive blood thinners to prevent clots, particularly if their heart function is significantly reduced. Low-dose aspirin is sometimes used if the coronary arteries show signs of widening.
Recovery and Long-Term Outlook
The good news is that most children with MIS-C recover well. Research from Children’s Hospital of Philadelphia found that heart function, which is often the biggest concern during the acute illness, begins improving within the first week of treatment and returns to normal within about three to four months. Roughly 81% of MIS-C patients experience reduced heart pumping during the acute phase, but contraction function normalizes by the three-to-four-month follow-up. A small percentage (about 7%) develop coronary artery aneurysms, which also tend to resolve relatively quickly.
Children are typically followed by a cardiologist for several months after discharge, with repeat imaging to confirm their heart has fully recovered. Most return to normal activities, including exercise and sports, once their cardiac function is confirmed normal.
How Common MIS-C Is Now
MIS-C has become dramatically less common. At its peak during the pre-Delta period (October 2020 through April 2021), more than 3,200 cases were reported in the U.S. at an incidence of about 6.79 cases per million person-months. By 2023, that figure had dropped to 0.11 cases per million person-months, a 98% decline from the peak. Only 117 cases were reported across the entire year.
Several factors likely explain this drop. Widespread immunity from both natural infection and vaccination has changed the landscape. A CDC study during the Delta wave found that two doses of the Pfizer-BioNTech vaccine reduced the risk of MIS-C by 91% in adolescents aged 12 to 18. The shift to Omicron subvariants, which cause less severe illness overall, has also contributed to the decline. While MIS-C still occurs, it is now rare enough that many pediatric centers see only a handful of cases per year.