Background: Little is known about the transmission dynamics of the B.1.617.2 (Delta) variant of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) among children and young adolescents. We investigated an outbreak in an Australian high school, with limited public health mitigation measures in place, to understand the school activities associated with transmission, and the role of young adolescents in spreading SARS-CoV-2.
Methods: All 1,164 school attendees were monitored for SARS-CoV-2 infection through their mandated 14-day quarantine period. A cohort study design was used to investigate the effect of contact with the index case in different classes on the transmission of SARS-CoV-2, and the effect of vaccination among household contacts on becoming infected by SARS-CoV-2.
Results: There were 48 outbreak cases, including 14 students and one teacher who likely acquired their infection at the school. Attack rates among students in the index case's classes ranged from 0% to 45%. The greatest risk of infection for students in the same grade attending a class with the index case were from the drama class (risk ratio, RR: 111.6; 95% confidence interval (95% CI): 14.88-837.19) and the personal development, health, and physical education class (RR: 7.45: 95% CI: 2.27-24.44). The overall household attack rate was 57%, and household contacts who were not fully vaccinated were 2.9 times more likely (95% CI: 1.07-7.87) to become cases than were effectively-vaccinated household contacts.
Conclusion: Children can play an important role in the transmission of the Delta variant of SARS-CoV-2 within schools and at home. Transmission in this outbreak was largely associated with active, practical lessons that had close contact between students. This study demonstrates that the absence of public health and social measures in a low-incidence context resulted in the rapid spread of coronavirus disease 2019 (COVID-19) within an educational setting. These findings reinforce the role of public health and social measures and vaccinations to reduce airborne transmission and to enable a safe face-to-face learning environment.
Keywords: COVID-19; SARS-CoV-2; adolescent; child; classroom; contact tracing; outbreak; risk factors; schools; transmission.
© Commonwealth of Australia CC BY-NC-ND.