A new University at Buffalo study conducted at John R. O’Shea Children’s Hospital is one of the first to find fewer cases of multisystem inflammatory syndrome (MIS-C) in children during an epidemic Omicron wave compared to a delta wave. . MIS-C is a rare but serious complication that occurs in children who have previously had COVID-19, and it has a fatality rate of nearly 1%. Published in the journal viruses Online Jan. 7, the study showed that those that occurred during Omicron were also milder than during Delta.
As shown in many other studies, during both waves, black children were disproportionately affected by MIS-C, and were more likely to be hospitalized with COVID-19. The authors attribute this to systemic and structural racial health inequalities and note that limited analysis beyond this observation was possible because the study was not directed at contributions to racial health disparities.
The study shows how the MIS-C landscape is constantly changing as new COVID-19 variants evolve. At the same time, the authors note, it’s hard to say what that means for the future.
“This is the hard question,” says Mark D. Hekar, MD, PhD, lead author, pediatric infectious disease specialist at UBMD and associate professor in the department of pediatrics in the Jacobs School of Medicine and Biomedical Sciences at the University at Buffalo. “Because we don’t know why the early strains of the virus caused more MIS-C and why the omicron caused less, it’s difficult to say whether future strains will be worse or better.”
Likewise, he says, it is difficult to predict what the current strain XBB.1.5 will do, as this variant is starting to flourish in national data and it takes weeks before MIS-C cases appear.
“Some recently published studies have indicated that MIS-C cases are becoming more severe, but those were based on 2021 data, before the Omicron wave really started,” Hekar notes.
“Our study is one of the first to show that during the change to omicron, MIS-C became increasingly milder and rarer,” he says. “This trend has continued and MIS-C is currently very rare according to anecdotal reports from colleagues around the country.”
However, he added that it is important to remain vigilant, as new strains of SARS-CoV2 can cause an increase in the incidence or severity of MIS-C.
Data from August 2021 to February 2022
The study retrospectively covered 271 patients admitted to Oishei Children’s Hospital from August 2021 to February 2022, which included the majority of delta wave and when Omicron wave (BA.1) was strongest.
One of the main strengths of the study is that a panel of three infectious disease specialists determined in each case whether a child had been hospitalized for COVID-19 or some other reason and then tested positive for the virus. . To avoid potential false positives, the UB study relied only on cases that tested positive through PCR testing.
The panel was created after Patrick O. Kenny, MD, first author and University at Buffalo Medical Fellow in Infectious Diseases, found that a number of children reported hospitalizations with only an incidental diagnosis of SARS-CoV2 on polymerase chain reaction (PCR) ). They were experiencing symptoms that were not common during the previous waves. This included diphtheria, which was first described by other groups, but also increased seizure rates, bleeding episodes and intra-abdominal inflammation including pancreatitis and hepatitis.
“It supported reports at the time that there was an increase in omicron hospitalizations of children, but those reports focused on global admissions data,” Hekar explains. “We wanted to take a deep look and have a thorough review of the clinical chart by three infectious disease physicians to decide whether a case was admitted due to COVID-19 or for some other reason and happened to have COVID-19.”
Hicar explains that this detailed approach helps explain how MIS-C may change over time, especially given the decrease in severe cases during omicron. The study found that during delta, MIS-C accounted for up to 12% of hospital admissions in Oishei while it accounted for only 6% of hospital admissions during omicron. Based on their data, the researchers estimate the risk of MIS-C from omicron in western New York to be 32% lower than during Delta.
The study notes that while there was an increase in Buffalo Children’s Hospital admissions during the Omicron wave, which was also nationwide, cases of both COVID-19 and MIS-C were generally less severe than during previous waves of the pandemic. . In addition, the length of hospital stay at Oishei Children’s Hospital as a result of either MIS-C or COVID-19 was relatively short during this period.
Researchers report that children who tested positive for COVID-19 and who did not have MIS-C during the omicron wave showed a wide range of symptoms, particularly among younger children, including seizures due to high fever, as well as croup and related conditions. By contrast, children who experienced MIS-C during omicron displayed a narrower spectrum of symptoms: they almost always had a fever along with abdominal or upper respiratory symptoms. The authors note that none of the patients in the study met even incomplete criteria for Kawasaki disease. Early in the pandemic, MIS-C was thought to be similar to Kawasaki disease.
Most patients have not been vaccinated
The authors indicate that the majority of children admitted to Oishei Children’s Hospital during the omicron period with COVID-19 or MIS-C were not vaccinated. Vaccines for children 12 years of age and older became available before the start of the study and were available for ages 5 to 11 during the study. Of the 107 children admitted with severe COVID-19 during omicron, vaccine status was recorded for 88 of them; Of these, five were fully vaccinated and one received a single dose. The others were unvaccinated.
Based on local county data showing that 33% of children under 18 had been vaccinated with the onset of the Omicron wave, rising to 42.1% by the end of the study period, the researchers calculated that the vaccines were between 87.8-91.7% effective in prevention. Hospitalization for either COVID-19 or MIS-C among children.
“Our data shows that even during major changes in the virus, from Delta to Omicron variants, vaccines can be very protective in preventing hospitalizations among children,” Hekar said.
In addition to Kenny and Hekar, the co-authors are Arthur J. Chang, MD, of Children’s Hospital and Medical Center of Omaha and Lorna Crabel, a fourth-year medical student at the Jacobs School.