Covid-19 Transmission - Evidence Studies

Many of you have been asking for evidence of the low transmission in schools and that children are not ‘super spreaders’ to help you make the argument for keeping schools open normally.
The UsforThem team have compiled a list of studies, articles and sources we hope will be useful.
We have also included evidence that asymptomatic transmission is not a main driver of outbreaks, including the recent study published in ‘Nature’.
Please contact us if we’ve missed anything out, and share with parents & carers, grandparents and teacher friends!
  • Children are less likely to become seriously ill from covid-19.
  • Children are also less likely to be infected (<5% of overall cases in Europe) and to transmit (children are not super spreaders).
  • For adults living with children there is no evidence of an increased risk of severe covid-19 outcomes.
  • 300k healthcare worker households in Scotland were less likely to get covid or to be hospitalised if they contained young children.
  • Evidence shows that transmission between children is limited and transmission in schools is very rare (staff more likely to transmit than children; child-staff extremely difficult to find).
  • Evidence indicates that asymptomatic individuals are not a main driver of transmission, which may explain the low level of transmission from children, who are less likely to be symptomatic.
  • Children are more likely to acquire infection at home than in school.
  • Infections in the wider community likely driving cases in schools (schools reflect what is going on in community).
  • School openings internationally have yielded fewer positive cases than expected.
  • Teachers not at elevated risk compared to other occupations.
  • Keeping schools closed is not supported by scientific evidence.
Asymptomatic Contacts
“Post-lockdown SARS-CoV-2 nucleic acid screening in nearly ten million residents of Wuhan, China”, 20 November 2020 No evidence of transmission from asymptomatic contacts: “All city residents aged six years or older were eligible and 9,899,828 (92.9%) participated…There were no positive tests amongst 1,174 close contacts of asymptomatic cases…Virus culture was carried out on samples from asymptomatic positive cases, and found no viable SARS-CoV-2 virus. All close contacts tested negative, indicating that the asymptomatic cases detected in this study were unlikely to be infectious.” https://www.nature.com/articles/s41467-020-19802-w7

“Infectiousness peaks early in COVID-19 patients, emphasising the need to rapidly isolate cases”, 20 November 2020 Systematic review and meta-analysis of three human coronaviruses published in The Lancet Microbe journal stated that no live virus (that can cause infection) was found in any type of sample collected beyond nine days of symptoms starting and people with SARS-CoV-2 are mostly likely to be highly infectious from symptom onset and the following five days. “Our findings are in line with contact tracing studies which suggest the majority of viral transmission events occur very early, and especially within the first 5 days after symptom onset.” https://medicalxpress.com/news/2020-11-infectiousness-peaks-early-covid-patients.html

“Contact Settings and Risk for Transmission in 3410 Close Contacts of Patients With COVID19 in Guangzhou, China”, 13 August 2020 Study tracked 3410 close contacts of 391 index cases grouped by symptoms; 305 showed no symptoms and infected just 1 person. Household contact was the main setting for transmission of SARS-CoV-2 (~83%). Attack rate highly correlated with symptom severity; minimal transmission from asymptomatic carriers. https://www.acpjournals.org/doi/10.7326/M20-2671 Paediatric Infectious disease expert Dr Alisdair Munro’s comment on the above study: “As children most likely to be asymptomatic, could explain low levels of transmission”, 18 August 2020 https://twitter.com/apsmunro/status/1295670209479618562?s=20

“A study on infectivity of asymptomatic SARS-CoV-2 carriers”, 13 May 2020 455 contacts who were exposed to family members, hospital staff, etc. with asymptomatic infection were tested. When tested at up to 14 days after exposure, all of the contacts were found to be free of the infection. “In summary, all the 455 contacts were excluded from SARS-CoV-2 infection and we conclude that the infectivity of some asymptomatic SARS-CoV-2 carriers might be weak…This finding implicates that there is not needful to worry unduly for asymptomatic or mild patients during the ongoing COVID-19 pandemic. Furthermore, excessive virus nucleic acid detection [testing] is unnecessary, which can relieve the pressure on public health resources.” https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7219423/

Childcare Settings
SAFE KiDS (Sandra Ciesek, MD), 4 November 2020 German 12-week study (pre-print) of 825 children (3 months to 8 years) and 372 staff members from 50 day care centres in Hesse detected no cases of covid found in children at low prevalence. https://www.medrxiv.org/content/10.1101/2020.11.02.20223859v1

Yale study, 16 October 2020 “While plenty of U.S. child care workers contracted COVID-19 in May and June, it wasn’t driven by whether they were working with children or not,” said Gilliam. The main factors in whether a child care worker got sick were the overall level of community transmission in the county where they lived, and race/ethnicity. https://news.yale.edu/2020/10/16/child-care-not-associated-spread-covid-19-yale-study-finds

Brown University epidemiologist Andrew Bostom, 5 October 2020 Professor has compiled a list of cases at US universities: Despite ~70K C19+ tests at 50 major US universities, barely any reported hospitalisations (i.e., 3), & no deaths. https://twitter.com/andrewbostom/status/1313162488955973634 September data covered in this article https://www.thecollegefix.com/bulletin-board/brown-u-epidemiologist-finds-zero-hospitalizationsfrom-26000-positive-covid-tests-for-college-students/
Primary & Secondary Schools: UK
“Teachers are NOT more likely to get coronavirus than other key workers” [and other professionals], 7 November 2020 ONS figures suggest there was no difference in infection rates between primary and secondary school teachers and other professionals between the start of September and mid-October. https://www.ons.gov.uk/peoplepopulationandcommunity/healthandsocialcare/ conditionsanddiseases/bulletins/coronaviruscovid19infectionsurveypilot/6november2020 https://www.dailymail.co.uk/news/article-8923855/Teachers-NOT-likely-coronavirus-key-workersofficial-study-finds.html

Public Health England study of England school reopening, 24 August 2020

  • 20,000 schools with 1 million children,
  • 67 single cases, 30 ‘outbreaks’:
  • -22/30 were staff-to-staff or staff-to-student transmission
  • -6/30 student-to-staff, student-to-student only 2 cases

Infections and outbreaks were uncommon in educational settings during the first month after the easing of national lockdown in England. The strong correlation with regional SARS-CoV-2 incidence emphasises the importance of controlling community transmission to protect educational settings. Additional interventions should focus on reducing transmission in and among staff members. https://www.medrxiv.org/content/10.1101/2020.08.21.20178574v1

  1. Only 0.01% of open educational settings had an outbreak
  2. Of over 1m children attending pre-school and primary school in June, just 70 children were affected
  3. Infections in the wider community likely driving cases in schools
  4. Children were more likely to acquire SARS-CoV-2 infection at home than in school


“No teachers have caught coronavirus from pupils anywhere in the world, claims SAGE adviser”, 22 July 2020 Professor Woolhouse, who sits on a sub-group of SAGE, told The Times it is ‘extremely difficult’ to find any instances of children spreading the virus to adults in schools, with no certain cases. https://www.dailymail.co.uk/news/article-8548461/No-proof-teacher-caught-Covid-19-pupilscientist-says.html

Edinburgh Professor of Infectious Disease Epidemiology Mark Woolhouse – very informative video presentation on schools and covid-19, 22 June 2020 Why close schools? To protect: -the children? But kids are at very low risk of this infection. -teachers and non-teaching staff? But they’re not at elevated risk. -the wider community? But it probably isn’t going to have much effect. https://media.ed.ac.uk/media/1_manc94er

“Children are not COVID-19 super spreaders: time to go back to school”, Drs. Alasdair Munro and Saul Faust (University of Southampton), 5 May 2020 Dr Alasdair Munro and Professor Saul Faust say it is time for classes to re-open as evidence from around the world shows that children have less chance of catching Covid-19 and are not “superspreaders” of the virus. Original article published by BMJ, 5 May: https://adc.bmj.com/content/105/7/618 Addendum inc. new data supporting authors’ view, 20 July: https://adc.bmj.com/content/early/2020/07/19/archdischild-2020-319908 News article 5 May: https://www.expressandstar.com/news/uk-news/2020/05/05/schools-shouldre-open-as-children-are-not-super-spreaders/

Sources to follow
Dr Alisdair Munro (University of Southampton) @apsmunro Twitter thread on paediatric studies: https://twitter.com/apsmunro/status/1298978413185703937?s=20

Website with comprehensive evidence summary of paediatric covid-19 literature: https://dontforgetthebubbles.com/evidence-summary-paediatric-covid-19-literature/

Executive summary of above: https://dontforgetthebubbles.com/evidence-summary-paediatric-covid-19-literature/

Reachwell – Researchers in Education and Adolescent Child Health and Wellbeing https://reachwell.org/ @sunilbhop @SelfHarmNotts

Prof Martin Kulldorff (Harvard Medical School, Swedish) @MartinKulldorff

Prof Emily Oster, Brown University. Covid-19 school dashboard: Filters on top let you look at age groups, learning models and state community rates https://covidschooldashboard.com/ @ProfEmilyOster

Swedish Public Health Agency, English CV-19 FAQs. For info on children and schools, scroll to end https://www.folkhalsomyndigheten.se/the-public-health-agency-of-sweden/communicabledisease-control/covid-19/

Covid-19 and Children
OpenSAFELY cohort study of 12 million adults in England, November 2020 Children do not increase the COVID risks to adults they live with. Analysis of the health records of 9m working age adults shows those living with secondary school-aged children had a small, 8% increased risk of being infected with the virus. But they were no more likely than adults without children to be admitted to hospital or die. Adults living with primary school-aged children were not even more likely to be infected, according to researchers from OpenSAFELY. https://opensafely.org/children/ https://news.sky.com/story/coronavirus-children-do-not-increase-risk-to-adults-they-live-with-newresearch-shows-12122573

“COVID-19 is not a driver of clinically significant viral wheeze and asthma”, 15 October 2020 133 children admitted to Leicester Hospital with viral/asthmatic wheeze and none tested positive. https://adc.bmj.com/content/early/2020/10/15/archdischild-2020-320776.full

“Sharing a household with children and risk of COVID-19: a study of over 300,000 adults living in healthcare worker households in Scotland”, 22 September 2020 Over 300,000 staff. Less likely to get Covid or to be hospitalised if household had young children. https://www.medrxiv.org/content/10.1101/2020.09.21.20196428v1

“COVID-19 in children: analysis of the first pandemic peak in England”, 12 August 2020 Studied children January-May 2020. Despite widespread testing, SARS-CoV-2 positivity rates throughout the pandemic peak were low in children compared with adults, including those presenting with acute respiratory infection in the community. Case-fatality rate in children with COVID-19 was <0.5% and there was no evidence of excess childhood mortality in children during the first wave of the COVID-19 pandemic in England. https://adc.bmj.com/content/early/2020/07/28/archdischild-2020-320042

“COVID-19 in Children and the Dynamics of Infection in Families” (Switz.), August 2020 39 child covid cases with positive family member – in 79% an adult was first, also adults more likely to catch than siblings. https://pediatrics.aappublications.org/content/146/2/e20201576

“Transmission dynamics of SARS‐CoV‐2 within families with children in Greece: A study of 23 clusters”, 7 August 2020 Study of 23 family clusters in Greece; no evidence of child-to-child or child-to-adult transmission. “While children become infected by SARS‐CoV‐2, they do not appear to transmit infection to others. Furthermore, children more frequently have an asymptomatic or mild course compared to adults” https://onlinelibrary.wiley.com/doi/full/10.1002/jmv.26394

“COVID-19 Transmission and Children: The Child Is Not to Blame”, Benjamin Lee, William V. Raszka. Pediatrics, 31 July 2020 “Almost 6 months into the pandemic, accumulating evidence and collective experience argue that children, particularly school-aged children, are far less important drivers of SARS-CoV-2 transmission than adults. Therefore, serious consideration should be paid toward strategies that allow schools to remain open, even during periods of COVID-19 spread. https://pediatrics.aappublications.org/content/146/2/e2020004879 Article about the study https://www.sciencedaily.com/releases/2020/07/200710100934.htm

Dr. Jeffrey Klausner, UCLA and Rajiv Bhatia, Stanford @drrajivb, 27 May 2020 “Because of school closures, most people have come to believe that children are a reservoir of COVID-19 infection and spread it to the old and vulnerable. That narrative is wrong and harmful.” https://www.thedailybeast.com/the-way-to-save-our-kids-is-to-reopen-our-schools-and-camps

“COVID-19 in Children and the Dynamics of Infection in Families”, Posfay-Barbe, Wagner, et al., 12 May 2020 Patients under 16 years old with SARS-CoV2 infection were identified by means of the Geneva University Hospital’s surveillance network. Since the onset of coronavirus disease (COVID-19) pandemic, children have been less affected than adults in terms of severity and frequency, accounting for <2% of the cases. Unlike with other viral respiratory infections, children do not seem to be a major vector of SARS-CoV-2 transmission, with most paediatric cases described inside familial clusters and no documentation of child-to-child or child-to-adult transmission. https://pediatrics.aappublications.org/content/pediatrics/146/2/e20201576.full.pdf

Cluster of Coronavirus Disease 2019 (COVID-19) in the French Alps, 11 April 2020 An infected child did not transmit the disease despite close interactions within schools, suggesting potential different transmission dynamics in children. https://academic.oup.com/cid/article/71/15/825/5819060

Primary & Secondary Schools: Rest of the World
National Public Radio, USA, 21 October 2020 Good international examples showing “It’s not that closing schools leads to a decrease in cases, or that opening schools leads to a surge in cases.” https://www.npr.org/2020/10/21/925794511/were-the-risks-of-reopening-schools-exaggerated? t=1604334807753

Start of New York City school year shows few cases, 19 October 2020 Start of the in-person school year yields surprisingly small number of positive cases. Out of 16,348 staff and students tested randomly by the school system in the first week of testing, the city has gotten back results for 16,298. There were only 28 positives: 20 staff members and 8 students. Mobile testing units at schools near Brooklyn and Queens neighborhoods that have had new outbreaks turned up only four positive of more than 3,300 tests conducted. https://www.nytimes.com/2020/10/19/nyregion/schools-coronavirus.html

US Covid school dashboard – Professor Oster, Brown University, 9 October 2020 Numbers for spread in schools are smaller than what many had forecasted. Predictions about school openings hurting the broader community seem to have been overblown. October in USA: Schools do not appear to be major spreaders of COVID-19. Data on almost 200,000 kids in 47 states from the last two weeks of September revealed an infection rate of 0.13% among students and 0.24% among staff. That’s about 1.3 infections over two weeks in a school of 1,000 kids, or 2.2 infections over two weeks in a group of 1,000 staff. Even in high-risk areas of the country, the student rates were well under half a percent. https://covidschooldashboard.com/ https://www.theatlantic.com/ideas/archive/2020/10/schools-arent-superspreaders/616669/ September: In-person teachers infection rate: 21 per 100k; Remote: 24 per 100k October: In-person: 19 per 100k; Remote: 17 per 100k https://www.npr.org/2020/09/23/915738935/new-dashboard-tracks-coronavirus-cases-in-schoolsacross-47-states

COVID-19 in Wisconsin High School Athletics, October 2020 Data from 30k students suggests that participation in sports is not associated with an increased risk of COVID-19 among Wisconsin high school student-athletes. No difference in COVID-19 incidence between student-athletes from schools with in-person versus virtual instruction. Findings agree with existing literature regarding COVID-19 severity in children, as none of the cases were reported to result in hospitalisation or death. Although 30% of the reported cases did not have an identified source, only 1(<0.5%) of the cases with a reported source was attributed to transmission during sports activities. https://ortho.wisc.edu/wp- content/uploads/2020/10/WI-HS-Sports-COVID-19-Summary.pdf

“Major coronavirus study in Spanish summer camps shows low transmission among children”, 26 August 2020 Of 1900 attendees, 39 had +ve PCR. This correlated with infection rates in their home areas. Contagion rates up to six times lower than those among the general population. https://english.elpais.com/society/2020-08-26/major-coronavirus-study-in-spanish-summer-campsshows-low-transmission-among-children.html

“COVID-19 in children and the role of school settings in COVID-19 transmission”, ECDC, 6 Aug 2020 Small proportion (<5%) of overall COVID-19 cases reported in the EU/EEA and the UK are among children (under 18s). Evidence suggests that re-opening schools has not been associated with significant increases in community transmission. Child to child transmission in schools appears uncommon. https://www.ecdc.europa.eu/en/publications-data/children-and-school-settings-covid-19- transmission

“Transmission of SARS-CoV-2 in Australian educational settings”, 3 August 2020 Tansmission rates were low in NSW educational settings during first COVID-19 epidemic wave, consistent with mild infrequent disease in 1.8m child population. Children and teachers did not contribute significantly to COVID-19 transmission via attendance in educational settings. https://www.thelancet.com/action/showPdf?pii=S2352-4642%2820%2930251-0

Office fédéral de la santé publique (Switzerland), 2 Aug 2020 Swiss study – schools started reopening on May 11th and account for 0.3% of the transmissions that could be traced, with two likely cases. https://www.bag.admin.ch/bag/fr/home/das-bag/aktuell/news/news-02-08-2020.html

“Transmission of SARS-CoV-2 following exposure in school settings: experience from two Helsinki area exposure incidents”, Dub et al, 20 July 2020 Keeping schools closed is not supported by scientific evidence, as seen in this study from Finland: “It is likely that transmission from children to adults is limited.” https://www.medrxiv.org/content/10.1101/2020.07.20.20156018v1.full.pdf

“Covid-19 in schoolchildren: A comparison between Finland and Sweden, The Public Health Agency of Sweden and Finnish Institute for Health and Welfare”, July 2020 “Outbreak investigations in Finland have not shown children to be contributing much in terms of transmission and in Sweden a report comparing risk of Covid-19 in different professions showed no increased risk for teachers.” Harvard Prof Martin Kulldorff wrote about this report: “The largest study is from Sweden. They never closed day-care/primary/middle schools, with zero COVID19 deaths among 1.8 million children ages 1-15. Among cases, 8 were admitted to ICU. So, low risk even with #OpenSchools at height of pandemic.” https://www.folkhalsomyndigheten.se/contentassets/c1b78bffbfde4a7899eb0d8ffdb57b09/covid-19- school-aged-children.pdf See further analysis and info on above report here http://inproportion2.talkigy.com/finnish_swedish_study_26jul.html Teacher risk tables here showing that risk for teachers is equal to or below that of the average profession – this full info is rarely seen as report is in Swedish only. http://inproportion2.talkigy.com/files/2020_07_RelativeCV19RiskPerOccupation_Sweden.pdf

“SARS-COV-2 Infection in primary schools in northern France: A retrospective cohort study in an area of high transmission, Institut Pasteur”, 23 June 2020 COVID-19 in primary schools: no significant transmission among children or from students to teachers. https://www.pasteur.fr/fr/file/35404/download Article about above https://www.pasteur.fr/en/press-area/press-documents/covid-19-primaryschools-no-significant-transmission-among-children-students-teachers