**2. Epidemiology**

MIS-C is a rare complication of pediatric COVID-19. It is described in <1 percent of children with confirmed SARS-CoV-2 infection [9]. Reports from the United States describe an incidence of 2 per 100,000 infected with COVID-19 under 21 years of age [11]. Despite these reports, the incidence of MIS-C can vary significantly depending on the infectious waves as well as the susceptibility of the population that is directly related to vaccination rates [12, 13]. It mainly affects children over 5 years of age. More than 70% of affected children have no associated comorbidities [14, 15].

### *Multisystem Inflammatory Syndrome in Children (MIS-C) DOI: http://dx.doi.org/10.5772/intechopen.110684*

It is described more frequently in some races (black, Hispanic, Latino); however, there may be biases influenced by their sociocultural reality [16]. The epidemiology of MIS-C differs from adult SARS-CoV-2 infection. Although most infected children have, like adults, asymptomatic or mild respiratory symptoms, it is in the severe presentation when a difference occurs, presenting as multisystem inflammation and not as severe pneumonia. Children, massively asymptomatic, could act as a reservoir and vector of viral infection, perpetuating the circulation of the new coronavirus in adults, favoring peaks of infection in them [17]. It is these peaks that affect the incidence of MIS-C, which has a temporal association with them. MIS-C appears a few weeks after the peak of SARS-COV2 infection. It is described between 2 and 8 weeks after the population infectious peaks, which means that MIS-C could correspond to an immune-mediated post-infectious disease. The emergence of SARS-COV2 variants has had an impact on the current occurrence of MIS-C. The Omicron wave is described as less severe in adults and with a lower incidence of MIS-C, which was reported worldwide. The Omicron waves showed that the pediatric population that was not fully vaccinated still decreased the incidence of MIS-C [18–22]. The impact of vaccination appears to influence not only the variant, but also the age at which MIS-C occurs, showing an epidemiological change with age shifting to younger children (< 5 years) who are not vaccinated [23, 24]. It is likely that this current decrease in the incidence of MIS-C is multifactorial, being related to the increasing exposure of the population to SARS-COV2, the lower viral circulation, and the massive adult and child vaccination, which probably generates variants with less possibility to create a hyperinflammation syndrome, maintaining the susceptibility of presenting the syndrome to populations with low vaccination rates.
