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  • CDC researchers found the MIS-C case rate in vaccinated U.S. children ages 12 to 20 years old was much lower than for unvaccinated people.
  • The findings show that in over 21 million children and adolescents who received one or more doses of the vaccine, there was only one reported case per million of MIS-C for this age group.
  • Symptoms of MIS-C include persistent fever, vomiting, abdominal pain, and diarrhea.

A new study of children who had received at least one dose of the COVID-19 vaccine found that occurrences of multi-system inflammatory syndrome (MIS-C) were rare and far less likely than for children who developed COVID-19 and were not vaccinated.

Researchers analyzed cases of MIS-C from December 2020 to August 2021 in vaccinated people ages 12 to 20 years old. They wanted to know whether the vaccine was linked to an increased risk for MIS-C.

The findings show that in over 21 million children and adolescents who had received one or more vaccine doses, there was only one reported case per million of MIS-C for this age group.

Centers for Disease Control and Prevention (CDC) researchers found that the MIS-C case rate in vaccinated U.S. children 12 to 20 years old was much lower than previous estimates for unvaccinated individuals in the same age group who had contracted the virus.

MIS-C has been documented in children who had COVID-19 and appeared to recover days, weeks, or even months before developing new symptoms.

“It’s a rare condition associated with COVID-19 infection in which multi-organ systems within the body become inflamed – inclusive of the heart, lungs, brain, eyes,” Dr. Kecia Gaither, double board certified in OB/GYN and maternal fetal medicine, and director of perinatal services at NYC Health + Hospitals/Lincoln in the Bronx, told Healthline.

Researchers wanted to see if MIS-C was also a risk for children if they had received a COVID-19 vaccine but had not developed the disease.

“We identified a small number of individuals aged 12–20 years with MIS-C after COVID-19 vaccination; most had laboratory evidence of past or recent SARS-CoV-2 infection,” study authors wrote.

The reported rate of MIS-C for those in the study who had not had previous COVID-19 disease was 0.3 cases per million vaccinated individuals.

A previous study cited by the researchers found that the risk of MIS-C after COVID-19 was 224 per million SARS-CoV-2 infections for children ages 11 to 15.

Study authors say more research is needed to determine whether vaccination was related to the development of the MIS-C illness in the rare cases they identified.

The team also noted the possibility that some of those cases involved children with other undiagnosed inflammatory conditions that developed after being vaccinated.

“As with COVID-19 illness, clinicians and researchers are still learning about MIS-C. Our investigation highlights the challenges in diagnosing MIS-C, the importance of considering alternative diagnoses, and the need to monitor for MIS-C illness,” study co-author Dr. Anna R. Yousaf said in a statement.

Currently, there is no clear relationship regarding who is at most risk for MIS-C after a COVID-19 case, said Dr. Ilan Shapiro, FAAP and chief health correspondent and medical affairs officer at AltaMed Health Services.

“We’ve also seen kids with neurological conditions and chronic health problems develop it, too,” Shapiro added. “It’s important to understand that COVID-19 doesn’t discriminate. Unfortunately, MIS-C can affect any child who contracts the virus.”

Shapiro noted an association with children who survive COVID-19 and develop MIS-C.

“Just like in the past, we have seen children develop Kawasaki syndrome, another inflammatory condition, after being infected with viruses,” he said.

“Compared to other years, we started to see thousands of these inflammatory symptoms emerge after COVID-19,” Shapiro added.

Gaither said children with MIS-C have a persistent fever with vomiting, abdominal pain, and diarrhea. More severe symptoms may include:

  • cardiac dysfunction
  • arrhythmias
  • respiratory compromise
  • headache, seizures, and confusion

“These symptoms are variable in presentation from child to child,” Gaither said. “And in essence represent a delayed response to COVID-19 infection,” she said.

Dr. Jin-Young Han, a pediatric infectious diseases expert at Weill Cornell Medicine, said MIS-C could occur in some children 2 to 6 weeks after acute COVID-19 disease.

Asked how the condition is treated and about the child’s prognosis, Han said the “vast majority” experience complete recovery with no long-term aftereffects.

“Most patients are treated with IVIG (intravenous immune globulin) and steroids, typically methylprednisolone,” he said.

Finding the reason MIS-C is associated with children who have COVID-19 is an area of intense study for many scientists and physicians, Han said.

“Although there are many theories, the answer is unknown at this time,” he said.

Shapiro emphasized the importance of giving the body the tools to defend itself.

He noted that children were kept home and not exposed to others at the start of the pandemic, shielding them from the virus.

“Once children returned to in-person learning, we experienced a large uptick of COVID-19 cases, and suddenly the concept of it’s ‘just a cold’ started to dissipate,” said Shapiro.

“We started to see more kids go to the hospital, the ER, and experience MIS-C, long COVID, and additional complications,” he continued. “Vaccination is the best protection for our kids to keep them safely in school where they can learn, develop friendships, and valuable social skills.”

New CDC research finds that COVID-19 vaccination is rarely associated with the development of MIS-C for children and adolescents.

Experts say that though MIS-C is potentially dangerous, most patients experience a complete recovery.

They also say that vaccination is the best way to protect children and keep them in school.