select search filters
roundups & rapid reactions
before the headlines
Fiona fox's blog

expert reaction to preprint from trial looking at daily testing instead of isolation for contacts of COVID-19 cases in schools and colleges

A preprint, an unpublished non-peer reviewed study, looks at data from a trial of the impact of a policy of daily testing for contacts of COVID-19 cases on attendance and COVID-19 transmission in English secondary schools and colleges.

This Roundup accompanied an SMC Briefing.


Prof Jon Deeks, Professor of Biostatistics and head of the Biostatistics, Evidence Synthesis and Test Evaluation Research Group, University of Birmingham, said:

“The Daily Contact Testing in Schools trial was set up to investigate whether testing students who are close contacts of a positive case with daily lateral flow tests is as safe as sending close contacts home to isolate, and whether such a policy leads to decreases in the numbers missing school.

“Schools were randomly allocated either to implement daily lateral flow testing of contacts (who if tested negative remained in class) or to follow the standard bubble isolation process.  Whilst this trial was large, recruiting 201 schools (of which 162 actively participated) the study does not provide conclusive findings.

“There are two key outcomes to look at here.  The first is whether contact testing led to a decrease in Covid related absence; the second whether it led to an acceptably small increase in Covid cases.

“During the study there were 590 Covid cases who had 10,226 contacts in school (average of 17 per child).  Introducing the testing policy did not substantially change Covid related absences – although it was lower in the arm with testing, the difference was too small to be confident that it had not been created by chance.  Part of the reason for the difference being small was that contact testing ended up being possible in only around half the contacts allocated to use it – due to the children refusing testing, being absent, or the school being closed because of the size of the outbreak.

“Covid infection rates were higher in the schools where contact testing was used, but again the small numbers mean that it is not possible to discern whether there is a real increase nor its size.  The authors state in their report that they were confident that the increase was less than 50%, which they regarded as acceptable, but  the rationale for this figure is not given.  Many would consider much smaller increases that this trial cannot exclude to be unacceptable, particularly when event rates are high, as currently the case.

“Previously we have not had any data on the accuracy of the Innova/NHS lateral flow test in UK school children.  This study is the first to estimate the ability of these lateral flow tests to detect infections in UK children, but is done using the different Orient Gene test, thought to be more sensitive than Innova.  However, of 60 cases in school contacts, the test only identified 32, thus the sensitivity is only 53%.  This illustrates the risk of using lateral flow tests, which only can detect high viral levels, to check whether contacts are infected.  As those that the test missed were close contacts they are likely to have been in the early stages of infection when viral levels are rising fast and the students are becoming infectious.

“Thus the study has failed to show that daily contact testing increases school attendance, nor provide data to show that it is safe, but has shown that lateral flow testing misses around half of the contacts who were infected by their friend at school.  In a rising pandemic wave with high infection rates in unvaccinated children, introducing such a policy seems unlikely to be a solution.”


Prof Sheila Bird, Formerly Programme Leader, MRC Biostatistics Unit, University of Cambridge, said:

“Randomization of 201 schools is a notable achievement for infection control but most 95% confidence intervals remain wide nonetheless.

“As secondary endpoint, the school-based RCT (p56 of supplementary material) compared performance of school-overseen Orient Gene antigen lateral flow device (LFD) versus contemporaneous PCR-test in 3,226 paired-tests, 60 of which were PCR-positive.  Of these 60, 32 were positive by Orient Gene which gave sensitivity for detection of infection as 53% (95% CI: 40% to 66%).  Better performance was observed when cycle-threshold was low.

“Overall, 80% of schools which had agreed to be randomized subsequently did participate.  Nonetheless, the RCT-analysts were given access – by randomized allocation only, I assume – to pupils’ (but not staff-members’) symptomatic PCR-positive-tests during the course of the RCT.  This was achieved because Department for Education apparently made pupils’ personal identifying information available to NHS Test and Trace for that purpose only.

“How schools and pupils were consented for this matters, of course.  Only four schools exercised an opt-out on pupils’ behalf, as shown in preprint’s Figure 1.”


Billy Quilty, Research Fellow in Infectious Disease Epidemiology at the Centre for Mathematical Modelling of Infectious Disease at the London School of Hygiene and Tropical Medicine:

“This trial provides valuable real-world evidence of the use of daily testing of contacts of confirmed Covid-19 cases, here used in the context of reducing school absences.  Validating modelling previously conducted for SPI-M/ SAGE [1-3], the study found no evidence of a difference in the rate of infection of contacts of those testing daily with lateral flow tests for 7 days while still attending school (1.5%) compared to those who stayed home for 10 days (1.6%).  Furthermore, no difference was observed in the overall infection rates in schools in each of the two study arms.  Given there were fears that daily testing could increase transmission in schools (e.g. through false negative test results), this is an encouraging result.

“Reductions in school absences were smaller than expected however, which the authors note may have been influenced by a 49.5% participation rate in daily testing and the ineligibility of individuals who were contacts of cases from outside the school setting.  Investigating and addressing the reasons for not participating will be key to the effectiveness of the policy.  A key outcome not investigated in this study is the reduction in workplace absences of parents who may otherwise have to take time off work to look after their isolating children.

“Overall, this trial indicates that daily testing could feasibly replace quarantine for contacts of cases in schools, and may reduce the disruption to children’s education as a result of the pandemic.  The results of further studies in workplaces and the general population will determine whether this policy may also be rolled out more widely to reduce the significant burden of quarantine in the UK.”

  1. SPI-M-O: Statement on Daily contact testing, 3 March 2021. Available from:
  2. Leng T, Hill EM, Thompson RN, Tildesley MJ, Keeling MJ, Dyson L. Assessing the impact of secondary school reopening strategies on within-school COVID-19 transmission and absences: a modelling study. medRxiv. 2021:2021.02.11.21251587. 
  3. Quilty BJ, Clifford S, Hellewell J, Russell TW, Kucharski AJ, Flasche S, Edmunds WJ; Centre for the Mathematical Modelling of Infectious Diseases COVID-19 working group. Quarantine and testing strategies in contact tracing for SARS-CoV-2: a modelling study. Lancet Public Health. 2021 Mar;6(3):e175-e183. doi: 10.1016/S2468-2667(20)30308-X


Prof James Hargreaves, Professor of Epidemiology and Evaluation, London School of Hygiene & Tropical Medicine, said:

This is an important study with promising results and a daily contact testing strategy within schools warrants consideration by policy makers.

“The research represents a huge effort on the part of the scientists, study staff and participating school communities.  It has some limitations, acknowledged by the authors, in particular a lower follow up rate for research surveillance in the control as opposed to the intervention arm of the study.  While this was not selected as the primary outcome of the study, because of concerns about differential participation rates between arms, it would have been reassuring to see higher follow up rates.

“Policy makers will need to consider a range of other factors.  First, the trial occurred during a period of low community incidence and impacts when community incidence are higher cannot be assumed.  Second, the research partly occurred prior to the period in which the more transmissible delta variant became the dominant variant circulating in the UK.  Third, if the daily contact testing strategy is to be considered for policy adoption, it will be essential to monitor and support coverage of existing control measures being implemented by schools, the wider testing programme in schools, and any new daily contact testing regimen.  Schools have taken on a huge additional burden of disruption and work in responding to COVID-19 and would need significant support to contribute to the success of the programme.  Fourth, maximising school confidence in the programme will be important – the study also identified a significant proportion of false negative results from lateral flow devices.

“Students and staff missing large amounts of school time due to isolating as contacts of confirmed Sars-Cov-2 infections, and the disruption to students, schools and carers that accompanies this, has been an important feature of the epidemic.  Identifying strategies that can maximise access to education while minimising the risk of transmission is essential.  This study compared a strategy of current normal isolation practice in English schools with a strategy in which contacts of confirmed Sars-CoV-2 cases were offered daily testing with lateral flow devices, which, if negative, allowed students to attend school.  In the study, rates of symptomatic Sars-CoV-2 infection in schools were relatively low, and similar, among students and staff in both arms of the trial, while students attended more school when offered daily tests as an alternative to isolation.  The authors conclude that this evidence suggests that a daily contact testing approach for schools should be considered as an alternative to current isolation policy for contacts of confirmed cases.”


Prof Jonathan Ball, Professor of Molecular Virology, University of Nottingham, said:

“It is always going to be tricky to define the relative effectiveness of isolation versus testing, as there are a lot of assumptions that need to be made.  That aside, what this study shows is that daily testing rather than isolation of contacts is effective in preventing onward transmission.  Crucially, it also highlights the unnecessary disruption that isolation rules have had on countless numbers of children.

“Isolation of contacts is an important weapon in infection control, but it is also crude.  Rapid testing circumvents needless isolation, and it should be used more widely.”


Prof Paul Hunter, Professor in Medicine, The Norwich School of Medicine, University of East Anglia, said:

“This is a cluster randomised trial with two arms to compare current exclusion practices in schools with a strategy around daily testing of contacts.  The study was designed to show whether the daily testing strategy led to less transmission than current exclusion.  For answering this question this was an entirely appropriate study design and the researchers conducted the study and analysed it appropriately.

“The author’s conclusions were that “There was no evidence that switching from isolation at home to daily contact testing increased rates of symptomatic COVID in students and staff” and based on the pre-print this is a sound conclusion.  But what this study cannot be used for is proving that either intervention actually reduces risk of transmission.  The conclusions could equally be that both interventions are highly effective or that both interventions have no value whatsoever.  It is a shame that the study didn’t have a do nothing control arm, though I suspect they would have struggled to get ethical permission for this, even if they had wanted to.

“Nevertheless I suspect when schools return some form of continuing control will be required and at least daily testing as in this study will have less harm on children’s education than the current exclusion policy, whether or not is has real benefit in controlling the epidemic.”



Preprint (not a paper): ‘A cluster randomised trial of the impact of a policy of daily testing for contacts of COVID-19 cases on attendance and COVID-19 transmission in English secondary schools and colleges’ by Bernadette C Young et al. was posted online at 00:01 UK time on Friday 23 July 2021.  This work is not peer-reviewed.



All our previous output on this subject can be seen at this weblink:



Declared interests

Prof Jon Deeks: “JD is an external advisor to the MHRA and the WHO, and leads the Cochrane reviews of the accuracy of tests for SARS-CoV-2 supported by funding from the Foundation for new Innovative Diagnostics.”

Prof Jonathan Ball: “No COIs.”

None others received.

in this section

filter RoundUps by year

search by tag