What Parents Need to Know About Multisystem Inflammatory Syndrome, an Illness Related to COVID-19 6 Shares Researchers are learning more about multisystem inflammatory syndrome in children (MIS-C), a rare COVID-related inflammatory illness that affects children and teens. Although the physical symptoms associated with the condition — which may include a rash, fever, bloodshot eyes, abdominal pain, vomiting, diarrhea, neck pain, fatigue, and, most concerning, heart problems — have been previously studied, it may affect patients' neurological well-being, too. Although medical experts do not specifically know what causes MIS-C, the Centers For Disease Control and Prevention (CDC) explained that it typically occurs in young people who have had COVID-19 or have been exposed to the virus. Moreover, the condition typically emerges between two and six weeks after a young person contracts COVID-19 and displays zero or mild symptoms. Research has found that children with more serious COVID-19 symptoms do not typically contract MIS-C.