In schools that have opened classrooms full or part time, there are 17 daily cases for every 100,000 students.

Among staff members in those schools, the daily case rate is 31, according to the database. Infection rates are even lower among just elementary schools, underscoring research that has suggested younger kids don’t transmit the virus as much as older ones. Oster’s database shows a daily case rate of 7 among students and 17 for staff members in elementary schools.

Add in reports from schools offering only virtual classes, and the daily case rate among students holds steady at 17, while the daily case rate among staff members falls slightly to 27. That could signal that holding in-person classes is contributing only a little — or not at all — to the spread of the virus among children and teachers.

It’s possible some children could unknowingly be infected, considering kids are less likely than adults to exhibit symptoms of covid-19. But even that hypothesis hasn’t borne out; when New York City performed more than 74,000 tests in 1,224 schools in October, just 45 students and 63 staff members tested positive.