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• Posted January 23, 2023

Omicron Silver Lining: Fewer, Milder Cases of MIS-C in Kids

The COVID-19 Omicron variant caused fewer cases of a rare but sometimes deadly complication for children than the earlier Delta variant did, new research shows.

"Our study is one of the first to show that during the change to Omicron, MIS-C has become milder and increasingly rare,"said senior researcher Dr. Mark Hicar, a University at Buffalo infectious disease specialist. "This trend has continued and MIS-C is currently quite rare, per anecdotal reports from colleagues across the country."

MIS-C (multisystem inflammatory syndrome in children) typically occurs two to six weeks after a child's COVID infection, and can cause dangerous inflammation in different organs throughout the body, according to the U.S. Centers for Disease Control and Prevention.

Nearly 1% of children who develop MIS-C die, the researchers said. The syndrome can also cause organ damage that can haunt children for the rest of their lives.

For the study, researchers tracked 271 patients admitted to Oishei Children's Hospital in Buffalo, N.Y., between August 2021 and February 2022. That span included the majority of the Delta wave, as well as the time when the Omicron wave surged the strongest.

During Delta, MIS-C comprised up to 12% of admissions at the children's hospital. But the syndrome only accounted for 6% of admissions during Omicron, the findings showed.

The risk of MIS-C from Omicron was about 32% lower than it was during Delta, the investigators concluded.

Overall, pediatric cases of both COVID-19 and MIS-C were generally less severe during the Omicron wave than they had been in previous waves of the pandemic, the researchers reported.

The team also noted that the majority of children admitted for COVID-19 or MIS-C had not been vaccinated.

Among 88 children admitted with COVID during the Omicron wave, only five were fully vaccinated and one had received a single dose. The rest were unvaccinated.

Based on local vaccination rates, the researchers calculated that the vaccines were as much as 92% effective in preventing hospitalizations for either COVID-19 or MIS-C.

"Our data show that even during major changes in the virus, from the Delta to Omicron variants, vaccines can be highly protective in preventing hospitalizations among children,"Hicar said in a university news release.

The new study was published online recently in the journal Viruses.

Hicar cautioned that it's difficult to say what these findings mean for the future.

"Since we don't know why the early strains of the virus caused more MIS-C and why Omicron causes less, it is hard to say if future strains will be worse or better,"Hicar said.

More information

The Mayo Clinic has more on MIS-C.

SOURCE: University at Buffalo, news release, Jan. 19, 2023