More than 10% of children in Japan who developed acute brain syndrome after infection with COVID-19 have died, results of a nationwide survey recently announced by a health ministry research team has shown.

The survey identified 34 cases of acute encephalopathy associated with COVID-19 infection among those under 18 between January 2020 and May 2022. The team analyzed 31 patients who did not have any underlying illnesses that could be responsible for causing the brain disease.

While 19 of the 31 children recovered, four died, and eight were confirmed with complications. Of the eight, five were reported as having severe aftereffects, including unconsciousness and being bedridden and in need of care.

Primary initial symptoms included seizures, which were experienced by about half of the patients, impaired consciousness, and abnormal speech or behavior.

"We would advise going to a hospital quickly ... if convulsions occurring with a fever don't stop in 10 minutes, loss of consciousness continues, or strange behavior is noticed," said Junichi Takanashi, a professor in pediatric neurology at Tokyo Women's Medical University Yachiyo Medical Center, who led the research team.

Most of the patients developed acute encephalopathy in January 2022 or later, when the omicron strain of the coronavirus became prevalent.

But there was no major difference in the ratio of those who developed the brain symptoms among COVID-infected children before and after 2022, indicating that omicron is not necessarily making it easier for the brain disease to develop, according to the study.

Development of acute encephalopathy among children is not limited to COVID-infection and is also known to afflict those who have contracted influenza.