September 2021

School Transmission Tracked

A case study published August 27 in the US CDC’s Morbidity and Mortality Weekly Report (MMWR) shows how quickly the highly contagious SARS-CoV-2 Delta variant can spread within a classroom of children too young to be vaccinated. The outbreak involved an unvaccinated Marin County, California (US), elementary school teacher who began showing COVID-19 symptoms on May 19, but who came to work the next 2 days, attributing the symptoms to allergies. During that time, the teacher read aloud to the class without wearing a mask, even though masks were required for staff and students while indoors. The teacher received a positive SARS-CoV-2 test on May 21 and informed the school on May 23. Several students became symptomatic on May 22, and the Marin County Department of Public Health (MCPH) initiated an investigation on May 26 to characterize the outbreak. Overall, 27 COVID-19 cases were identified, including the teacher. Among the teacher’s 24 students—all of whom were too young to be eligible for vaccination—12 of 22 who were tested received positive results between May 23-26. Notably, 8 out of 10 students who sat in the 2 front rows closest to the teacher became infected, representing an extremely high attack rate of 80%.

–Johns Hopkins Center for Health Security

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