newsGP – ‘Significant’ decrease in MIS-C risk under Omicron

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Omicron causes far fewer cases of childhood multisystem inflammatory syndrome (MIS-C), a new study from Denmark suggests.


The syndrome, also known as pediatric multisystem inflammatory syndrome – temporally associated with SARS-CoV-2 (PIMS-TS), has affected more than 100 children in Australia since the pandemic started.


It is one of the most serious possible manifestations of COVID-19 in children.


The Danish study, published this week in the open access medical journal of the American Medical Association JAMA Networkalso reinforces the evidence that vaccination offers significant protection against the disease.


The details came from a prospective, population-based cohort study with patients aged 0-17 years from all pediatric departments of Denmark. This year, the survey ran from January 1 to March 15.


Among 583,618 children and adolescents infected with COVID-19, the researchers identified 12 cases of MIS-C — one from a cohort of 267,086 vaccinated individuals and 11 among the remaining unvaccinated patients.


There were no MIS-C cases among 31,516 estimated individuals with reinfections.


The researchers from Aarhus University Hospital state that Omicron was the dominant variant in 95% of the registered cases.


Philip Britton, Associate Professor of Child and Adolescent Health at the University of Sydney, said the research is reassuring.


He says the findings reinforce data previously emerged in a pre-print study from the UK that suggested the condition is less common in Omicron cases than in Delta, which in turn caused fewer cases than Alpha†


“This should be seen as an encouraging finding for the country,” Associate Professor Britton told IPS newsGP† “It was always fairly rare on the order of one in 2,000 or 3,000 infections in children.”


The data from Denmark suggest the condition is likely to affect less than 1 in 10,000 children in the Omicron wave, even at the higher end of estimates for unvaccinated patients.


Associate professor Britton says there is uncertainty about what caused the lower numbers.


However, he notes that existing studies, including the recent one from Denmark, distance themselves from the suggestion that the lower numbers of MIS-C cases are due to population immunity.


“They claim that if you exclude the vaccinated group and take the infection rates at the population level, you still see a decreased frequency of MIS-C, suggesting something is Omicron-specific,” he said.


There’s also “plausibility” in the idea, associate professor Britton believes, that the lower complications are virus-specific, which he says would be a welcome development.


“In that sense, if we go the Omicron pathway in terms of the future of SARS-CoV-2, that’s good for those working in child health,” he said.


Associate professor Britton added that there is not enough current evidence to conclude why vaccination appears to provide significant additional protection against the disease.


‘It is not entirely clear whether this protective effect is because [the vaccine] protects you from infection,” he said.


Authors of the Danish study suggest that the effect of the vaccines on the immune system is probably critical in people with breakthrough infections.


“This may be due to vaccine-induced modulation of the immune system that makes it less prone to hyperinflammation following SARS-CoV-2 infection,” they write.


The authors also reported that MIS-C was not observed in reinfections, although they acknowledge that only 6% of infected individuals in the study had confirmed reinfection.


“Such a reduced risk after reinfection has not yet been reported,” they said.


Also for associate professor Britton, no firm conclusions could be drawn from the study about the risk of MIS-C in reinfected patients. He also notes that one of the study’s limitations is that only a small number of MIS-C cases are involved and said it could be challenging to collect more evidence.


“Measuring reinfection rates in populations is difficult,” he said.


‘Because there is no absolute serological marker of infection or reinfection, you really have to have observed those infections in real time.


“So the data is reassuring, but it would be good to see those kinds of findings from other places as well.”


Until relatively recently, almost no cases of MIS-C were found in Australia due to the low prevalence of COVID-19.


Associate Professor Britton says the country has been lucky enough to learn from experiences elsewhere and says no deaths have been attributed to MIS-C in Australia so far.


“Contrary to early data from abroad, in our experience in Australia it is a minority of cases that end up in intensive care,” he said.


“That’s probably because we took advantage of our colleagues’ early experience abroad to learn how to manage this condition.”


Despite the reassuring signs that MIS-C may be less common in Omicron, associate professor Britton said it’s important to remain vigilant given the high number of existing cases.


Similarly, while Australia has one of the highest COVID vaccination rates in the world, children ages 5-11 are easily the least protected cohort, with only 39.07% have received two doses at the time of publication.


Adolescents aged 12-15 have the second lowest COVID vaccination rate, with only 80% registered as fully vaccinated.


“While this will be rare, we will continue to see cases in the near future that require hospital management,” he said.


GPs may be the first point of contact for families with a child who has developed a new fever, then a fever, along with other features of this [syndrome]†


‘GPs should ask questions of people who come to their practice with persistent fever and any characteristics of’ [MIS-C] about previous COVID infection as a way to identify these cases.”


Associate Professor Britton said the peak risk period is about 3-5 weeks after SARS-CoV-2 infection.


However, he emphasized the small risk and efficacy of the existing treatment.


“The general public should be reassured that Australian clinicians are now very familiar with this condition, that we are working together in children’s hospitals across the country to support its management,” he said.


“And almost all children respond very quickly to appropriate and early treatment.”



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