No evidence of association between schools and SARS-CoV-2 second wave in Italy
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Abstract
Background
During 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.
Methods
We 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 R t 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.
Findings
From 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 R t was not uniform. Reciprocally, school closures in two regions where they were implemented before other measures did not affect the rate of R t decline.
Interpretation
Our 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 context
Evidence before this study
The 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. Italy’s 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 study
We 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 evidence
These 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.
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SciScore for 10.1101/2020.12.16.20248134: (What is this?)
Please note, not all rigor criteria are appropriate for all manuscripts.
Table 1: Rigor
Institutional Review Board Statement not detected. Randomization not detected. Blinding not detected. Power Analysis not detected. Sex as a biological variable not detected. Table 2: Resources
Software and Algorithms Sentences Resources Statistical analyses were performed with Statistical Analysis System Version 9.4 (SAS Institute, Cary, NC, USA) or with OriginPro 2021 (OriginLab, Northampton, MA, USA). Statistical Analysis Systemsuggested: (Statistical Analysis System, RRID:SCR_008567)SAS Institutesuggested: (Statistical Analysis System, RRID:SCR_008567)OriginProsuggested: NoneResults from OddPub: We did not detect open data. We also did not detect open code. Researchers are encouraged to share open data when …
SciScore for 10.1101/2020.12.16.20248134: (What is this?)
Please note, not all rigor criteria are appropriate for all manuscripts.
Table 1: Rigor
Institutional Review Board Statement not detected. Randomization not detected. Blinding not detected. Power Analysis not detected. Sex as a biological variable not detected. Table 2: Resources
Software and Algorithms Sentences Resources Statistical analyses were performed with Statistical Analysis System Version 9.4 (SAS Institute, Cary, NC, USA) or with OriginPro 2021 (OriginLab, Northampton, MA, USA). Statistical Analysis Systemsuggested: (Statistical Analysis System, RRID:SCR_008567)SAS Institutesuggested: (Statistical Analysis System, RRID:SCR_008567)OriginProsuggested: NoneResults from OddPub: We did not detect open data. We also did not detect open code. Researchers are encouraged to share open data when possible (see Nature blog).
Results from LimitationRecognizer: We detected the following sentences addressing limitations in the study:Moreover, authors warn on the limitations of their estimates: for example, they could not consider the different precautions related to the reopening of schools taken by some countries, such as physical distancing within classrooms and masking procedures; they did not consider the impact of school holidays and the effect of reopening different school levels (e.g., elementary and middle schools). Finally, authors analyze the impact of given NPIs by comparing Rt from two arbitrarily drawn periods before and after the implementation of the given NPI. While this approach might be more practical when comparing multiple countries, it is less informative than our analysis performed overall the Rt curve. Interestingly, we found that Rt started declining even before the implementation of any NPI, in all the regions analyzed. In certain cases, like the Province of Trento, the nationally implemented NPI entered in force after Rt had declined below the threshold of 1. These results, while perhaps surprising, are in line with findings from the group of Merler, who analyzed the impact of the national March-May lockdown on Rt in Italy. While they concluded that lockdown reduced Rt and brought it below 1, they admitted that the decline in Rt had started well before the national lockdown was implemented. Visual inspection of their published Rt curves indeed confirms that this extreme NPI did not affect the slope of Rt decline 37. Our study is strengthened by the several sources of data used. ...
Results from TrialIdentifier: No clinical trial numbers were referenced.
Results from Barzooka: We did not find any issues relating to the usage of bar graphs.
Results from JetFighter: We did not find any issues relating to colormaps.
Results from rtransparent:- Thank you for including a conflict of interest statement. Authors are encouraged to include this statement when submitting to a journal.
- Thank you for including a funding statement. Authors are encouraged to include this statement when submitting to a journal.
- No protocol registration statement was detected.
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SciScore for 10.1101/2020.12.16.20248134: (What is this?)
Please note, not all rigor criteria are appropriate for all manuscripts.
Table 1: Rigor
Institutional Review Board Statement not detected. Randomization not detected. Blinding not detected. Power Analysis not detected. Sex as a biological variable not detected. Table 2: Resources
Software and Algorithms Sentences Resources Statistical analyses were performed with Statistical Analysis System Version 9.4 (SAS Institute, Cary, NC, USA) or with OriginPro 2021 (OriginLab, Northampton, MA, USA). Statistical Analysis Systemsuggested: (Statistical Analysis System, RRID:SCR_008567)SAS Institutesuggested: …SciScore for 10.1101/2020.12.16.20248134: (What is this?)
Please note, not all rigor criteria are appropriate for all manuscripts.
Table 1: Rigor
Institutional Review Board Statement not detected. Randomization not detected. Blinding not detected. Power Analysis not detected. Sex as a biological variable not detected. Table 2: Resources
Software and Algorithms Sentences Resources Statistical analyses were performed with Statistical Analysis System Version 9.4 (SAS Institute, Cary, NC, USA) or with OriginPro 2021 (OriginLab, Northampton, MA, USA). Statistical Analysis Systemsuggested: (Statistical Analysis System, RRID:SCR_008567)SAS Institutesuggested: (Statistical Analysis System, RRID:SCR_008567)OriginProsuggested: NoneResults from OddPub: We did not detect open data. We also did not detect open code. Researchers are encouraged to share open data when possible (see Nature blog).
Results from LimitationRecognizer: We detected the following sentences addressing limitations in the study:
Moreover, the author themselves raise several words of caution on the limitations of their estimates: for example, they could not consider the different precautions related to the reopening of schools taken by some countries, such as physical distancing within classrooms and masking procedures; they did not consider the impact of school holidays and the effect of reopening different school levels (e.g., elementary and middle schools). Finally, authors analyze the impact of given NPIs by comparing Rt from two arbitrarily drawn periods before and after the implementation of the given NPI. While this approach might be more practical when comparing multiple countries, it is less informative than our analysis performed overall the Rt curve. Interestingly, we found that Rt started declining even before the implementation of any NPI, in all the regions analyzed. In certain cases, like the Province of Trento, the nationally implemented NPI entered in force after Rt had declined below the threshold of 1. These results, while perhaps surprising, are in line with findings from the group of Merler, who analyzed the impact of the national March-May lockdown on Rt in Italy. While they concluded that lockdown reduced Rt and brought it below 1, they admitted that the decline in Rt had started well before the national lockdown was implemented. Visual inspection of their published Rt curves indeed confirms that this extreme NPI did not affect the slope of Rt decline 37. Closure of schools has ...
Results from TrialIdentifier: No clinical trial numbers were referenced.
Results from Barzooka: We did not find any issues relating to the usage of bar graphs.
Results from JetFighter: We did not find any issues relating to colormaps.
About SciScore
SciScore is an automated tool that is designed to assist expert reviewers by finding and presenting formulaic information scattered throughout a paper in a standard, easy to digest format. SciScore checks for the presence and correctness of RRIDs (research resource identifiers), and for rigor criteria such as sex and investigator blinding. For details on the theoretical underpinning of rigor criteria and the tools shown here, including references cited, please follow this link.
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