With the beginning of the new semester, schools in Japan are heading into uncharted waters as they battle a delta-driven explosion in COVID-19 cases, prompting some parents to decide not to send their children back to the classroom.

In some municipalities, elementary, middle and high schools resumed classes last week after a monthlong summer vacation. But for many students, Wednesday marked the first day back at school.

The school restart has coincided with a recent surge in the number of teens and preteens infected with the coronavirus, igniting controversy over whether it’s safe to allow pupils back into schools.

Health ministry data shows that the weekly total of those age 19 and younger who tested positive for COVID-19 had hit 30,427 nationwide as of Thursday, a nearly sixfold jump from the 5,535 about a month ago when the summer break had just begun.

This has led some concerned parents to take the rare step of having their children stay at home despite the start of the school year.

The recent spread of the virus has prompted the education ministry to put together guidelines that spell out the circumstances under which schools in regions subject to a state of emergency and other strengthened anti-virus measures should consider shutting down classes.

According to the guidelines, if two or more students are confirmed to be infected, then the whole class should be suspended for five to seven days. The guidelines go on to clarify that even if there is only one child who has tested positive, suspension is still encouraged if there are multiple close contacts or multiple students in the same class who exhibit flu-like symptoms.

If there are other classes like this in the same grade, students in that particular grade should all stay at home, according to the guidelines. If the suspensions must expand across different grades, then the entire school needs to shut down.