Researchers and European authorities said the absence of any notable clusters of infection in reopened elementary schools so far suggested that children aren’t significant spreaders of the new coronavirus in society.

They acknowledged that their findings might change with the onset of winter and cold weather, and a recent outbreak at a Jerusalem high school affecting students and staff was a reminder of the higher risk to teenagers and adults.

But Denmark, Austria, Norway, Finland, Singapore, Australia, New Zealand and most other countries that have reopened classrooms haven’t had outbreaks in schools or day-care centers.

In Denmark, the opening of schools had no impact on the progress of the epidemic, said Tyra Grove Krause, a senior official with the State Serum Institute, the country’s disease control agency.