Eurosurveillance | Secondary transmission of COVID-19 in preschool and school settings in northern Italy after their reopening in September 2020: a population-based study eurosurveillance.org/content/10.280…
This is a very nice study because they tested all school contacts of index cases irrespective of symptoms.
There were multiple measures implemented in schools to reduce crowding and maintain physical distance between students
Under these conditions, secondary attack rates were very low in primary schools, somewhat higher in middle and high schools (6.5%).
This is lower than what is generally reported in other settings like workplaces or households.
Most interesting is the fact that 50% of secondary cases were asymptomatic, that transmission occurred also from asymptomatic as well as presymptomatic index cases.
Some limitations; sequencing was not performed, so cannot be sure cases within clusters were indeed linked. Some secondary cases may in fact have been tertiary cases, given long time-window btw test positivity.
At 14 day testing interval, some cases may have been missed.
What we can learn from this study is that screening of classmates of school index cases, irrespective of symptoms can help us identify double the number of cases identified by symptom based testing alone.
Given that these asymptomatics can pass the virus on, identifying these can help reducing spread within schools and to outside school contacts.
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