Photo/Illutration A child receives a COVID-19 vaccine in Okayama city on March 11. (Asahi Shimbun file photo)

Some children have developed severe symptoms of COVID-19 after catching the novel coronavirus despite having no underlying conditions, it has been reported.

The number of children developing severe symptoms has been increasing as the number of COVID-19 cases involving children is rising to an unprecedented level due to the spread of the Omicron variant.

Considering “the eighth wave” as a possibility, experts stress the importance of being vaccinated. 

The number of COVID-19 patients 19 or younger was 5.49 million as of Sept. 20, according to the health ministry’s data.

Analysis based on the ministry’s data shows the cumulative number of COVID-19 patients 19 or younger from September to December 2020 was 14,000.

The figure for 2021 was 220,000.

This means most of the COVID-19 patients who are children have appeared after the Omicron variant became widespread.

There were only three COVID-19-related deaths among those 19 or younger by the end of 2021 before rising to 31 as of Sept. 20.

It has been reported that with more children catching the virus, some have even been hospitalized after developing moderate or severe symptoms.

Experts said it is worrying that some of the children needing hospitalization have no underlying conditions.

The Japanese Society of Intensive Care Medicine studied 220 COVID-19 patients who are 19 or younger across Japan who received treatment, including hospitalization, after developing moderate or severe symptoms requiring oxygen administration between March 10 and Aug. 15.

It found that 150, or 68 percent, had no underlying conditions.

The sixth wave started during the study period, between March 10 and Aug. 15.

The society separately studied 152 COVID-19 patients 19 or younger who were hospitalized in or after late June.

It found that many of them were younger children, with half being of a preschool age, 30 percent being elementary school students and 10 percent being infants 1 or younger.

It found that more children were developing symptoms such as acute encephalopathy, which can lead to impaired consciousness, or febrile convulsions caused by a high fever.

Hiroshi Kurosawa, a pediatrician at Hyogo prefectural Kobe Children’s Hospital, who conducted the study, said that since the Omicron variant has become dominant, the number of COVID-19 cases in children has increased, which has led to a rise in children who develop moderate or severe symptoms regardless of whether they have underlying conditions.

“As any child could develop moderate or severe symptoms, appropriate measures taken by the whole of society, such as wearing masks in closed spaces, are desirable,” he said.

Since the Omicron variant has become widespread, more children infected with the novel coronavirus have been hospitalized for developing croup syndrome and its accompanying symptoms, such as severe respiratory conditions, convulsions, vomiting and dehydration, according to Tomohiro Katsuta, associate professor of pediatric infectious diseases at St. Marianna University School of Medicine.

Croup syndrome is known for causing a distinctive type of cough.

Katsuta said as restrictions on going out or doing other activities are being lifted, “Receiving the vaccine is more important now.”

Experts have found the vaccine for children between 5 and 11 causes fewer side effects than for those 12 or older, according to the Japan Pediatric Society.

They also discovered that the vaccine for children between 5 and 11 is 40 to 80 percent effective in preventing severe symptoms from COVID-19.

Administering the COVID-19 vaccine to children 5 to 11 has started in Japan.

In the United States, pharmaceutical companies asked a regulator to authorize
boosters that target the BA.5 subvariant for children 5 to 11 at the end of September.

It is expected the same application will be made in Japan, too.

The health ministry officials, however, said that they assume the vaccine used now for children 5 to 11 is effective against the Omicron variant to some extent.

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