Influenza outbreaks continue to be reported at schools across Japan, pushing into May an epidemic that typically subsides by March.

At some schools, entire classes were temporarily closed after hundreds of students and teachers were infected with the flu virus.

One health expert said the easing of measures against COVID-19 is likely contributing to the spread of influenza.

The average number of influenza patients per regularly reporting medical institution in the week through May 14 was 1.36, according to the health ministry.

The figure represented a decrease from 1.7 reported in the previous week, but it still exceeded 1, the threshold for an epidemic, the ministry said.

Niigata Prefecture had the highest average number for the week, at 5.64 patients, followed by 4.3 in Yamagata Prefecture, 2.36 in Miyazaki Prefecture, 1.62 in Oita Prefecture, 1.44 in Hyogo Prefecture, and 0.96 in Tokyo.

Among all nursery, elementary, junior high and high schools across the nation, three were temporarily closed and 70 canceled classes, even for entire grades.

In the three years through 2022, when COVID-19 spread, there was no flu epidemic in Japan.

But the ministry declared a nationwide flu epidemic at the end of December last year. The spread of influenza reached a warning level by the end of January and peaked in early February.

It has since been on a declining trend, but the epidemic for the first time since 2019 has continued into May.

CROWDED FESTIVALS

Many group infections occurred around school events, such as sports festivals.

At a high school in Miyazaki city, one student was confirmed infected with influenza on May 9. But since the number of patients was so limited, the school decided to hold its weekend sports festival as scheduled.

As is normal for such festivals, the students were boisterous when they celebrated their victories together, according to the city government.

The flu virus spread rapidly at the school, and 394 students and teachers were confirmed infected on May 15, the Monday after the festival. The number hit 491 the following day.

The school decided to close operations from May 15 to 22.

In a high school in Oita city, 47 students were absent due to influenza on May 11, two days after their sports festival. The number of absentees surged to 403 on May 15, and the school was shut down until May 16.

About 2,000 students cheered loudly and engaged in close-quarter events, such as the tug-of-war, at the festival, according to the school.

“An influenza epidemic is unusual for this time of year when the weather is getting hotter,” an official of the Hyogo Prefectural Board of Education said.

In the prefecture, flu cases at schools have increased since late April. Classes were canceled at six schools from May 8 to 14.

The Tokyo metropolitan government said on May 18 that 104 students and teachers were confirmed to have contracted influenza at a school in the city of Chofu.

Thorough measures had been taken in Japan to prevent the spread of the novel coronavirus, including mask wearing and social distancing. As a side benefit of such action, flu infections did not spread.

But Japan on May 8 downgraded the severity of COVID-19 to the same category as seasonal influenza. Since then, more people have been venturing outdoors and gathering in crowds at public places.

“Over the past three years or so, there have been fewer opportunities for exposure to the flu virus, which has now made it easier for infections to spread, especially among younger generations who have less immunity to the virus,” said Yosuke Aoki, a member of the Influenza Committee of the Japanese Association for Infectious Diseases and a professor at the Faculty of Medicine, Saga University.

Measures against COVID-19 have been relaxed in schools from this academic year. Students can decide on their own if they will wear masks at their schools.

“If our guard against the novel coronavirus is lowered, our guard against influenza also weakens,” Aoki said.

He said effective measures against the flu are the same as those for COVID-19, such as wearing masks, ensuring proper ventilation in rooms and thoroughly washing hands.

But he pointed out that medicine exists to treat influenza.

“There is no need to return to strict infection control measures like those during the pandemic,” he said.

(This article was written by Yuichiro Yoneda, Takako Fuchizawa and Rie Kowaka.)