Six hundred and fifty probable cases of acute hepatitis of unknown aetiology in children have been reported to WHO from 33 countries in five WHO Regions between 5 April and 26 May 2022.
The aetiology of this severe acute hepatitis remains unknown and under investigation; the cases are more clinically severe and a higher proportion develops acute liver failure compared with previous reports of acute hepatitis of unknown aetiology in children. It remains to be established whether and where the detected cases are above-expected baseline levels. WHO assesses the risk at the global level as moderate.
Factors such as increased susceptibility amongst young children following a lower level of circulation of adenovirus during the COVID-19 pandemic, the potential emergence of a novel adenovirus, SARS-CoV-2 co-infection or a complication of previous SARS-CoV-2 infection, leading to superantigen-mediated immune cell activation, proposed a causal mechanism of multisystem inflammatory syndrome in children need to be further investigated.