(Updated on January 7, 2021)
I have written a couple of previous blog posts explaining that in-person K-12 instruction, at least on a part-time basis, did not seem to be contributing significantly to the spread of the current pandemic. Social scientists usually hesitate to reach definitive conclusions based on research studies, because we understand the limitations of those studies and that any particular study, or even a whole group of studies using a similar methodology, could suggest a conclusion that turns out to be incorrect. However, at this point, there is such a significant accumulation of evidence from so many different sources that children can attend school, at least on a part-time basis, without contributing significantly to the spread of the pandemic that it seems safe to conclude that almost all K-12 schools should be open at the beginning of 2021, at least with a hybrid instruction model.
I will review a timeline of that evidence in this blog post. First, though, it is important to make a distinction between the populations included in different studies. Some studies have focused only on the relationship between in-person instruction and COVID-19 cases in school-aged children, while other studies have considered the relationship between in-person instruction and COVID-19 cases in the entire community (usually, the county or state). Studying the relationship only with school-aged children can be preferable because the confounding effect of other social distancing measures is likely smaller than it is when we consider the entire community. However, limiting the population to school-aged children fails to consider possible effects on teachers and other school staff and the possibility that children could be asymptomatic spreaders of the virus and it also doesn’t consider indirect effects of in-person instruction on the spread of the pandemic – when children are back in school, parents may go out more and contribute more to the spread. Therefore, it seems important to consider the results from both types of studies and, in particular, to see if results differ between the types.
On May 14, a group of researchers from the University of Kentucky published an article in Health Affairs (https://www.healthaffairs.org/doi/full/10.1377/hlthaff.2020.00608), one of the leading health policy journals, analyzing the effects of various social distancing policies on the COVID-19 case growth rate across U.S. counties during the initial spread of the pandemic. Although they found that both shelter-in-place orders and restaurant and entertainment business closures significantly reduced the case growth rate, they found that school closures did not significantly affect the case growth rate.
On June 8, a large group of researchers from the University of California Berkeley published an article in Nature (https://www.nature.com/articles/s41586-020-2404-8), one of the leading journals across all scientific disciplines, analyzing the effects of various social distancing policies on the COVID-19 case growth rate across U.S. states and across localities in five other countries (China, France, Iran, Italy, and South Korea) during the initial spread of the pandemic. In the United States, they found that stay-at-home orders, closing businesses, work-from-home policies, and “other social distancing” measures all significantly reduced the case growth rate, but they found that school closures did not significantly affect the case growth rate.
On July 8, a group of researchers from the University of Pennsylvania published a study in Clinical Infectious Diseases (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7454446/pdf/ciaa923.pdf), a leading infectious diseases journal, analyzing the effect of emergency declarations and school closures on the COVID-19 adjusted mortality rate across U.S. states during the initial spread of the pandemic. They found that each day of delay in declaring an emergency was related to a 5% increase in the mortality rate and that each day of delay in closing schools was related to a 6% increase in the mortality rate. However, this study did not control for other social distancing measures and the authors acknowledged that “both emergency declarations and the timing of school closures may be a proxy for the degree to which a state began to officially and unofficially implement significant social distancing. . . . Thus, our results may reflect how quickly states responded to news about the size and severity of the spreading pandemic, with emergency declarations and school closures being among the first official nonpharmaceutical interventions, rather than protective effects specific to either intervention itself.” I agree with that interpretation and do not consider this study to show that closing schools reduced the mortality rate.
On September 23, researchers from Brown University and Qualtrics first released their National COVID-19 School Response Data Dashboard (https://statsiq.co1.qualtrics.com/public-dashboard/v0/dashboard/5f78e5d4de521a001036f78e#/dashboard/5f78e5d4de521a001036f78e?pageId=Page_c0595a5e-9e70-4df2-ab0c-14860e84d36a), which they have continued to update. Their dashboard initially included data from only about 550 schools, but now includes data from more than 9,000 schools. They have not published any reports analyzing the dashboard data. However, Emily Oster, the lead Brown University researcher on the project, has been featured in numerous news stories since then and, based on the dashboard data, she has consistently expressed the opinion that schools do not seem to be major spreaders of COVID-19 (https://www.theatlantic.com/ideas/archive/2020/10/schools-arent-superspreaders/616669/; https://www.washingtonpost.com/opinions/2020/11/20/covid-19-schools-data-reopening-safety/?arc404=true ).
On September 27, I published a blog post (http://blogs.uis.edu/garywreinbold/2020/09/27/effect-of-k-12-instruction-types-on-reported-covid-19-cases-and-deaths-in-illinois-counties/) analyzing the effects of different K-12 instruction types on COVID-19 cases and deaths in Illinois counties. These results have not yet been peer-reviewed, so they should be interpreted more cautiously than studies published in high-quality journals. I compared three groups of Illinois counties based on the instruction types that they used at the beginning of the school year: counties with a majority of students in districts with in-person instruction, counties with a majority of students in districts with hybrid instruction, and counties with a majority of students in districts with online-only instruction. I found that majority online-only instruction and majority hybrid instruction both significantly reduced the number of new cases in the county as compared with majority in-person instruction. However, there was not a significant difference between majority online-only instruction and majority hybrid instruction in the number of new cases and there was not a significant difference between any of the three groups of counties in the number of new deaths.
On October 1, the Swiss non-profit organization Insights for Education released a report (https://blobby.wsimg.com/go/104fc727-3bad-4ff5-944f-c281d3ceda7f/20201001_Covid19%20and%20Schools%20Six%20Month%20Report.pdf) analyzing the relationship between school reopenings and new COVID-19 cases across countries. Their report also was not peer-reviewed. Also, they considered only the unadjusted relationship between school reopenings and cases, without using statistical methods to control for other factors, which gives me even less confidence in their findings. However, they concluded that “there has not been any consistent relationship between school closure dates and the reported cases of infection in the population.”
On October 2, a group of Spanish researchers released a report (https://biocomsc.upc.edu/en/shared/20201002_report_136.pdf) analyzing the relationship between reopening schools and the COVID-19 case growth rate across Spanish autonomous communities (which are similar to states). Their report also has not yet been peer-reviewed and, like the Insights for Education report, it considers only the unadjusted relationship between school reopenings and cases. However, after considering the relationships between school reopenings and both cases within the entire population in each autonomous community and cases by age group in each autonomous community, they concluded “that the global incidence evolution suggests no significant effects of the reopening of schools, and that, in most cases, there is either absence of increase in cases of pediatric ages or a slight increase that is compatible with current diagnostic effort in the schools.”
On October 16, two British researchers published an article in Science (https://science.sciencemag.org/content/370/6514/286), another leading journal across all scientific disciplines. Based on their review of the evidence about COVID-19 and schools, they concluded that “existing evidence points to educational settings playing only a limited role in transmission when mitigation measures are in place.” As a result, they expressed the opinion that “school closures should be undertaken with trepidation given the indirect harms that they incur. Pandemic mitigation measures that affect children’s wellbeing should only happen if evidence exists that they help because there is plenty of evidence that they do harm.”
On November 6, the Illinois Department of Public Health first released contact tracing data (Contact Tracing | IDPH (illinois.gov)), which it has continued to update weekly. I explained in a November 14 blog post (http://blogs.uis.edu/garywreinbold/2020/11/14/what-can-school-boards-learn-from-idphs-contact-tracing-data/) that schools were in the lowest risk category in the initial data release, with only about 0.24% of potential exposures resulting in outbreaks. Overall, I observed that the contact tracing data were not that helpful in making decisions about school instruction types, but that nothing in those data disagreed with the general conclusion that K-12 schools have not been a major contributor to the spread of the pandemic.
On November 19, at the White House’s coronavirus briefing, Robert Redfield, the Director of the Centers for Disease Control and Prevention (CDC) explained: “The infections that we’ve identified in schools, when they’ve been evaluated, were not acquired in schools. They were actually acquired in the community and in the household. . . . The truth is for kids K-12, one of the safest places they can be from our perspective is to remain in school.” (Trump Opposes Lockdown in Virus Surge But Birx Urges Vigilance – Bloomberg).
Finally, on December 15, a group of researchers from the University of Mississippi, Mississippi State University, and the CDC published a report (Factors Associated with Positive SARS-CoV-2 Test Results in Outpatient Health Facilities and Emergency Departments Among Children and Adolescents Aged <18 Years — Mississippi, September–November 2020 (cdc.gov)) in Morbidity and Mortality Weekly Report, which is a well-respected CDC publication, although it is not peer-reviewed. The authors studied 397 children in Mississippi who had taken COVID-19 tests between September 1 and November 5, including 154 children with positive test results and 243 children with negative test results. The children with positive tests were much more likely to have had close contact with a person with COVID-19 and to have attended gatherings with persons outside their household in the two weeks prior to the test. However, in-person school or child-care attendance was not associated with a positive test result.
Therefore, a variety of approaches have been used to analyze the relationship between in-person K-12 instruction and the spread of the pandemic and virtually all of those approaches have concluded that children can attend school, at least on a part-time basis, without contributing significantly to the spread of the pandemic. Of course, there may still be unusual cases where particular districts or schools should not offer any in-person instruction, such as if the virus is spreading rapidly in the community, if hospital or intensive care unit capacity in the community is critically low or, if the school’s facilities don’t allow in-person instruction to be safely offered even to smaller classes of students. However, other than those exceptional cases, it seems safe to conclude that almost all K-12 schools should be open at the start of 2021, at least with a hybrid instruction model.
A few new resources have been published relating to this issue since my original post, so I will briefly address those sources:
In late December 2020, a group of researchers from the University of Washington and Michigan State University posted a working paper (https://caldercenter.org/sites/default/files/WP%20247-1220_updated_typo.pdf) analyzing the relationship between school instruction types and new COVID-19 case rates in Michigan and Washington during September, October and November. Again, this paper has not yet been peer reviewed, so it should be interpreted more cautiously than some of the studies discussed above that were published in leading journals. However, these researchers found that hybrid instruction did not have any effect on COVID-19 case rates in Michigan (for any counties, regardless of their prior case rates), that in-person instruction did not have any effect on case rates in Michigan in counties with low to moderate case rates (below the 95th percentile) and that hybrid or in-person instruction (considered together) did not have any effect on COVID-19 case rates in Washington in counties with low to moderate case rates (below the 75th percentile). In counties with high case rates (above the 95th percentile in Michigan and above the 75th percentile in Washington), their results were inconclusive, as some methods found that in-person instruction (in Michigan) or hybrid or in-person instruction (in Washington) resulted in higher case rates, while other methods did not. Overall, this study suggests that hybrid instruction, in particular, has not significantly increased case rates in most counties, except possibly in counties with high pre-existing case rates.
On December 30, the California Department of Public Health posted its own summary of the existing evidence of the effects of school reopenings on the pandemic (https://www.cdph.ca.gov/Programs/CID/DCDC/Pages/COVID-19/Safe-Schools-for-All-Plan-Science.aspx) as part of the Governor’s effort to persuade California elementary schools to reopen in February (https://www.politico.com/states/california/story/2020/12/30/newsom-pushes-california-school-reopening-plan-that-could-begin-in-february-1351652). The CDPH summary concludes: “Core mitigation strategies are necessary for safe and successful schooling. If those mitigation strategies are implemented as several layers of safety, elementary schools can be safe workplaces for teachers and other staff and safe learning environments for children.” Considering that California has been one of the worst-hit states over the past month and has almost no available intensive care unit capacity in most parts of the state, it is notable that even they are attempting to reopen schools.
On January 4, three researchers from Tulane University published a report (https://www.reachcentered.org/uploads/technicalreport/The-Effects-of-School-Reopenings-on-COVID-19-Hospitalizations-REACH-January-2021.pdf) examining the effects of school reopenings on COVID-19 hospitalizations across the United States. Again, this report has not yet been peer-reviewed and the authors took some novel approaches that will likely benefit from peer review, so their results should be interpreted carefully at this point. However, the authors found no effect of school reopenings on COVID-19 hospitalizations for counties with low to moderate hospitalization rates (below the 75th percentile) and their results were inconclusive for counties with high hospitalization rates, with one method showing a small positive effect of school reopenings on hospitalization rates for those counties and another method showing no effect. Overall, this study suggests that school reopenings have not significantly increased hospitalization rates, except possibly in counties with high pre-existing hospitalization rates.
These additional resources add further support to the conclusion that almost all K-12 schools should be open at the start of 2021, at least with a hybrid instruction model, except in exceptional circumstances like those discussed above.