Limitations

The quantitative analysis for this report was based on data as recorded in PHESS, which is the source of truth for COVID-19 reporting in Victoria. Additional data cleaning was undertaken over the course of several weeks specifically for this project, involving over 19,000 PHESS records. Limited information is available about contacts in comparison to cases, and key details were missing from many records, for example demographic characteristics. A number of analyses could not be conducted due to incomplete data, for example an analysis of transmission dynamics within classes and year levels rather than at the level of the entire school. The definition of ‘upstream’ and ‘downstream’ cases is based on diagnosis date and symptom onset date; however this does not necessarily indicate transmission. Two people from the same household may share a common exposure, and due to the variable incubation period of SARS-CoV-2, one may get sick over a week after the other. This does not necessarily indicate that one gave SARS-CoV-2 infection to the other, they simply had a later disease onset date. In addition, a member of a school community might acquire SARS-CoV-2 in an unrelated outbreak, but they might still be counted as a ‘downstream’ case of the school because the source of their infection cannot be identified with the data available in this analysis. The use of ‘upstream’ and ‘downstream’ in this report should be understood in that context. We used DHHS definitions according to standard outbreaks reporting practice, which was developed by DHHS prior to this project. The datasets used in this analysis are part of an active ecosystem and are subject to daily revisions, as data are updated in PHESS and reporting practices change in response to public health needs. The research team did not have complete oversight over historical data recording, cleaning and reporting practices, which influence the dataset on which these analyses were conducted. Some variables were not usable due to variation in recording practices over time. The final data cut was taken on the morning of Tuesday 15 September 2020 and the results in this report are final as of that date. Subsequent changes to data in PHESS will not be reflected in this report, for example data that related to events that occurred in August, some of which may still be under revision as public health actions are completed. The DHHS analysis findings in this report are also subject to a number of other limitations: ● Guidance for contact tracing methodology changed during the pandemic and could have resulted in differences in data collected over time. ● Testing criteria only included symptomatic persons initially, which would have led to an underestimate of cases and transmission. Nevertheless, we found that there were very few serious cases of COVID-19 (which is likely to be complete in its reporting) associated with ECEC and schools and who required hospitalisation. ● As many cases are asymptomatic, particularly children, the “first identified” case may not have been the “true” first case in the outbreak. Therefore the “true” first case may have been missed (not tested) or have cleared the infection undetected. ● Many confirmed cases associated with outbreaks in ECEC and schools will have been the result of transmission outside the educational facility, including via other outbreaks. ● The impact of school transmission migiation strategies, could not be evaluated, apart from school closures, as it was not known how individual schools implemented these.