Many schools across the nation reopened Monday after summer vacations were shortened to allow students to catch up on classes missed when schools closed due to the novel coronavirus pandemic.

The shortest break decided by municipal authorities was only nine days. Usually, students in Japan take vacation in summer for more than a month.

Students wearing face masks started arriving at Ushioda Elementary School in Yokohama, near Tokyo, around 8 a.m. Their summer vacation had been shortened to roughly half its usual length.

“I was unable to go enjoy myself at the swimming pool because of the coronavirus,” said Naoya Hirasawa, 12.

Schools are required to take steps to reduce the risk of heat exhaustion as well as to prevent coronavirus infections. Temperatures have risen rapidly in recent days, with the mercury hitting 35 degrees Celsius or more in many locations.