Initially, contacts and close contacts were placed on home leave until test results were known (in the case of contacts) and for 7 days from the last exposure (in the case of close contacts).
We divided contacts into 2 groups by contact level: those in close contact (close contacts) and those in contact except for close contacts (non–close contacts) with the index case-patient.
A negative binomial regression model with a log link identified factors associated with higher positivity rates among all contacts (close and non-close contacts) and close contacts.
Positivity rates among all contacts were 2.04% (95% CI 1.96%–2.11%) (2,914/143,184), among close contacts were 3.06% (95% CI 2.83%–3.31%) (629/20,546), and among non–close contacts were 1.86% (95% CI 1.79%–1.94%) (2,285/122,638).
Field epidemiologic investigations corroborate this low infection risk at schools, indicating that the transmission route constitutes only 4% of elementary schools, 6% of junior high schools, and 4% of high schools (22).

SARS-CoV-2 Infection in School Settings, Okinawa Prefecture, Japan, 2021–2022