Different regions of the country are still at different points in the Omicron wave, and it will take some time before scientists have a clearer picture of what the variant has meant for MIS-C cases overall.

Most MIS-C cases have not been fatal, but just last week, the Wisconsin Department of Health Services reported that a 10-year-old from the southeast part of the state died within the past month from MIS-C.

“We want to share this information with the CDC with hopes that we can ultimately find out what’s causing this and what we could do to further prevent MIS-C,” Haupt said.

One thing is certain about MIS-C: “It always follows the same pattern,” said Dr. Roberta DeBiasi, Infectious Disease Division chief at Children’s National Hospital in Washington, DC. “It’s always two to six weeks after we see the spike from whatever variant it is, and then we’re on the lookout for MIS-C. And then, sure enough, it comes.”

In Washington, DeBiasi said, her hospital has had 30 Omicron-related MIS-C cases. But each wave has brought with it fewer cases. With the first wave, DeBiasi said, they treated about 100 kids with MIS-C, and with Delta, it was about 60.

It’s unclear exactly why there have been fewer cases, but she theorizes that vaccines — now authorized for children 5 and older — may have helped.

“The older kids are much less represented among the MIS-C cases now, and that makes sense because they’re vaccinated, and there are plenty of studies now showing that vaccination reduces the risk of MIS-C cases just like it reduces the risk of hospitalization and severe disease,” she said.

At Children’s Hospital of Colorado, workers are seeing about two or three cases of MIS-C a week, despite what Dr. Pei-Ni Jone described as “a ton” of Covid-19 cases. She said some of the MIS-C patients have been vaccinated, but the vast majority are not.

“The MIS-C children, we thought we may see an uptick with Omicron, but we haven’t. It’s very similar for us with the Delta surge,” the cardiology specialist said. “It’s really unknown what’s driving the MIS-C cases.”

At the University of Pittsburgh Medical Center, Dr. Marian Michaels watched the many-fold increase in Covid infections and hospitalizations in her area with deep concern, but the spike in MIS-C cases hasn’t come. “Luckily, in our area we are not seeing a surge,” she said. “I’m very grateful.”

Michaels said she regularly talks with other doctors as a part of a CDC surveillance network, and with Omicron, it’s been “a mixed bag.” Some hospitals have seen a spike in MIS-C cases, but many have seen only a handful.

At Children’s Hospital in Los Angeles, they too are watching patient numbers closely, but so far, so good.

“Children’s Hospital Los Angeles has yet to see a large spike in MIS-C cases following the surge of Omicron cases in the community,” pediatric cardiologist Dr. Jacqueline Szmuszkovicz of the Heart Institute at Children’s Hospital Los Angeles wrote in an email to CNN.

In December and January, the hospital treated 22 MIS-C patients. In February, it’s been three, with two hospitalized.

“Because we know MIS-C may begin weeks after a child is infected with SARS-CoV-2, we are continuing to be vigilant and waiting to see what the next few weeks bring,” Szmuszkovicz said.

At Lurie Children’s Hospital of Chicago, Dr. Ami Patel, a pediatric infectious disease physician, said workers have seen a steady uptick in MIS-C cases since the end of December. But this is “still relatively lower numbers overall compared to the winter 2020 surge,” she said. During the Delta surge, the hospital saw “relatively few” MIS-C cases.

But there has been a spike at Seattle Children’s. “Approximately 15% of the total MIS-C cases we’ve seen since March 2020 have occurred since mid-December 2021, when Omicron emerged as the main variant. These numbers suggest that MIS-C is increasing with Omicron,” Dr. Michael Portman, director of research in the Division of Cardiology, wrote in an email to CNN.

Texas Children’s in Houston saw the peak in Omicron cases January 7, a little later than in other regions, so workers there still don’t know what MIS-C case load to expect.

There haven’t been any “dramatic increases” — at least, not yet, according to Dr. Jim Versalovic, pathologist-in-chief at the hospital.

Health care providers there have treated more than 280 MIS-C cases since the pandemic began, with two-thirds serious enough that they’ve needed critical care.

The biggest number of MIS-C cases happened between mid-September and mid-October, with the Delta variant. “We’re not quite at that level yet,” Versalovic said. Instead, they’re seeing about one case per day every two to three days.

At UH Rainbow Babies and Children’s Hospital in Cleveland, MIS-C cases seemed to follow much quicker after the spike in Omicron infections than with previous Covid-19 waves. That may not have been unique to the Omicron variant, though, said Dr. Claudia Hoyen, a pediatric infectious disease specialist there.

“I think the reason that it seems so bad was that we were in the Delta surge when Omicron came,” she said.

At Cincinnati Children’s Hospital Medical Center, Dr. Patty Manning said, workers have seen two or three cases of MIS-C a week during Omicron — “possibly less than what we would expect, given the spike of Covid cases in general that we saw.”

She said that could be due to the success of vaccinations, or it could be something specific about Omicron causing fewer MIS-C cases. “It’s unclear at this moment. But we’re never wanting to get comfortable,” Manning said. “Parents still need to be vigilant.”

What to watch for with MIS-C

Pediatricians say that if kids have Covid-19, parents should watch for MIS-C symptoms, typically four to six weeks after the infection. They may look like a return of Covid symptoms or totally different. If the symptoms get worse, they need treatment.

“Children have died in the United States because they didn’t get to emergency rooms fast enough,” Versalovic said.

Doctors said they have learned a lot about how to treat MIS-C. At Jone’s hospital in Colorado, many of the children with MIS-C have not needed to be hospitalized for quite as long as kids were at the beginning of the pandemic.

Doctors are much better at recognizing MIS-C, said UPMC’s Michaels. “Treatment right up front has just been critical.”

Some children may also need breathing or cardiac support like ventilation or ECMO treatments.

“The long-term follow-up will also be essential to understand how kids do long-term and to understand, from an immune system perspective, what’s going on,” said Michaels, who is involved in several MIS-C studies. “It will also be important to understand from an immune system standpoint, the ones that still are having an effect long-term. Why is that in that case versus another child who was perfectly healthy before the virus? Why would they not have such a good outcome?”

Most children seem to recover well

Jone said that at Colorado Children’s, most children get better and do not seem to have lingering effects.

“The first MIS-C children we saw were in May of 2020. So they already had their one follow-up, and all of those kids in 2020 have done very, very well,” Jone said.

The best approach with MIS-C, doctors said, is for children not to catch Covid-19 in the first place.

“It’s a very scary, serious condition,” Manning said. “We want to avoid and prevent it at all costs.”

That means getting all kids vaccinated if they’re eligible. Children are still the least-vaccinated of any eligible age group.

There’s no vaccine authorized for children under 5, but parents can protect them by making sure every adult around them is fully vaccinated.

“We do need to vaccinate. There is no infection in the world that has ever gone away just because of having herd immunity from natural disease. Measles didn’t go away from herd immunity,” Michaels said. “Protecting yourself and your loved ones by being immunized is really critical.”