This past June, the New England Journal of Medicine published two articles describing a then-newly identified complication of COVID-19 infection in children, which the CDC had named Multisystem Inflammatory Syndrome in Children, or MIS-C. At the time, it was unclear whether this complication was unique to children. However, the CDC’s Morbidity and Mortality Weekly Report (MMWR) recently published a case series summarizing 27 cases of a similar condition in adults.
To review, the CDC defined MIS-C as fever for at least 1 day, severe illness involving 2 or more organ systems (heart, kidneys, lungs, blood, gut, skin and/or brain and spine) requiring a hospital stay, and either laboratory evidence of current or recent COVID-19 infection or exposure to COVID-19 within the previous 4 weeks in a child or young adult aged less than 21 years. In this case report, the CDC defined the multisystem inflammatory syndrome in adults (MIS-A) similarly aside from occurring in adults age 21 years or older. Although the adults ranged in age from 21 to 50 years, half of the patients described in this report were less than 35 years old.
Most of the adults with MIS-A described in the MMWR case series had heart disease, nausea, vomiting, diarrhea or rash, similar to the children with MIS-C in the earlier reports. Interestingly, only about half of the adults had severe lung disease or shortness of breath typical of COVID-19 infection, and nearly a third of them had lab evidence of recent but not current COVID-19 infection; similar findings had been reported in children with MIS-C. Finally, about two-thirds of children previously described with MIS-C and about half of adults in this MIS-A report had no high-risk conditions before getting sick.
This new information has several interesting implications. First, MIS-C and MIS-A are so similar that it may be reasonable to combine the two conditions into a single multisystem inflammatory syndrome associated with COVID-19. However, it may also make sense to gather more data on MIS-A and do an in-depth analysis of any differences between children and adults before making such a change.
The relatively young age of adults in the MIS-A group suggests either that this is a condition of children and younger adults or that healthcare providers may be less likely to recognize it in middle aged and older adults. Additionally, most of the children and adults described with this condition did not have any known high risk conditions for COVID-19; likewise, people younger than 30 have lower rates of hospitalization and death from COVID-19 than middle aged and older adults. Could it be that there is something unique to how younger, healthy people respond to COVID-19 that simultaneously puts them at lower risk for severe disease but higher risk for this multisystem inflammatory syndrome? Alternatively, are people with severe COVID-19 infection less likely to come down with this multisystem inflammatory syndrome?
Finally, previous studies have suggested that MIS-C peaks about a month after COVID-19, and about one in three adults with MIS-A had lab evidence of recent but not current COVID-19 infection. This suggests that the multisystem inflammatory syndrome associated with COVID-19 may be a long-term effect of COVID-19 infection. As I mentioned previously, if this condition is in fact an abnormal immune response to COVID-19 (as has not yet been proven, only suggested) then this raises concerning questions about whether a COVID-19 vaccine could also cause a similar complication. None of the COVID-19 vaccine studies in the United States currently include children, but most if not all include younger adults. I would hope that researchers and U.S. Food and Drug Administration (FDA) reviewers closely examine these studies for any sign of an association of COVID-19 vaccines with a multisystem inflammatory syndrome before they are approved. The FDA recently issued revised COVID-19 vaccine guidelines calling on Phase 3 studies to follow up with participants for at least 2 months after receiving their last dose; this should provide enough time to find evidence of multisystem inflammatory syndrome in vaccinated people and compare against unvaccinated people who get COVID-19.
In sum, this study answers a key question about whether the multisystem inflammatory syndrome associated with COVID-19 is limited to children or also occurs in adults. However, it raises several other important questions not only about this condition but about COVID-19 and potential COVID-19 vaccines. I feel confident that physicians and scientists will continue to examine these questions and hopeful that COVID-19 vaccine researchers and FDA regulators will consider them.
Stay healthy and keep wearing those masks, and let me know in the comments if you have any other questions about this condition,
😷 Dr. B