No evidence of association between schools and SARS-CoV-2 second wave in Italy.

BackgroundDuring the Covid19 pandemic, school closure has been mandated in analogy to its known effect against influenza, but it is unclear whether schools are early amplifiers of Covid19 cases. MethodsWe performed a cross-sectional and prospective cohort study in Italy. We used databases from the Italian Ministry of Education containing the number of new positive SARS-CoV-2 cases per school from September 20 to November 8, 2020 to calculate incidence among students and staff. We calculated incidence across each age group using databases from the Veneto Region system of SARS-CoV-2 cases notification in the period August 26- November 24, 2020. We used a database from the Veneto Region system of SARS-CoV-2 secondary cases tracing in Verona province schools to estimate number of tests, the frequency of secondary infections at school by type of index case and the ratio positive cases/ number of tests per school institute using an adjusted multivariable generalized linear regression model. We estimated the reproduction number Rt at the regional level from the Italian Civil Protection of regional SARS-CoV-2 cases notification database in the period 6 August-2 December 2020. FindingsFrom September 12 to November 7 2020, SARS-CoV-2 incidence among students was lower than that in the general population of all but two Italian regions. Secondary infections were <1%, and clusters of >2 secondary cases per school were 5-7% in a representative November week. Incidence among teachers was greater than in the general population. However, when compared with incidence among similar age groups, the difference was not significant (P=0.23). Secondary infections among teachers were more frequent when the index case was a teacher than a student (38% vs. 11%, P=0.007). From August 28 to October 25 in Veneto where school reopened on September 14, the growth of SARS-CoV- 2 incidence was lower in school age individuals, maximal in 20-29 and 45-49 years old individuals. The delay between the different school opening dates in the different Italian regions and the increase in the regional Covid19 reproduction number Rt was not uniform. Reciprocally, school closures in two regions where they were implemented before other measures did not affect the rate of Rt decline. InterpretationOur analysis does not support a role for school opening as a driver of the second wave of SARS-CoV-2 epidemics in Italy, a large European country with high SARS-CoV-2 incidence. Research in contextO_ST_ABSEvidence before this studyC_ST_ABSThe role of schools and at large of children as amplifiers of the Covid19 pandemics is debated. Despite biological and epidemiological evidence that children play a marginal role in Sars-CoV-2 spread, policies of school closures have been predicated, mostly based on the temporal coincidence between school reopening in certain countries and Covid19 outbreaks. Whether schools contributed to the so called "second wave" of Covid19 is uncertain. Italys regionalized calendar of school reopening and databases of positivity at school allows to estimate the impact of schools on the increase of Sars-CoV-2 that occurred in autumn 2020. Added value of this studyWe found that incidence among students is lower than in the general population and that whereas incidence among teachers appears higher than that in the general population, it is comparable to that among individuals of the same age bracket. Moreover, secondary infections at school are rare and clusters even less common. The index case of a secondary teacher case is more frequently a teacher than a student. In Veneto, during the first phase of the second wave incidence among school age individuals was low as opposed to the sustained incidence among individuals of 45-49 years. Finally, the time lag between school opening and Rt increase was not uniform across different Italian regions with different school opening dates, with lag times shorter in regions where schools opened later. Implications of the available evidenceThese findings contribute to indicate that Covid19 infections rarely occur at school and that transmission from students to teachers is very rare. Moreover, they fail to support a role for school age individuals and school openings as a driver of the Covid19 second wave. Overall, our findings could help inform policy initiatives of school openings during the current Covid19 pandemic.