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expert reaction to latest interim results from the REACT-1 study on COVID-19 prevalence across England

A preprint, an unpublished non-peer reviewed study, reports on the latest data from the REACT-1 study on COVID-19 spread across England (swabs taken between 24 June and 5 July 2021).

This Roundup accompanied an SMC Briefing.


Dr Peter English, Retired Consultant in Communicable Disease Control, Former Editor of Vaccines in Practice, Immediate past Chair of the BMA Public Health Medicine Committee, said:

“Scientific knowledge advances in various ways. While we often think of experiments – phase III trials, randomised controlled trials, and so on – it also advances through surveillance and observational studies.

“The REal-time Assessment of Community Transmission-1 (REACT-1) study is one of the latter. A sample of the population provided a throat swab for testing for the SARS-CoV-2 virus, and completed a questionnaire.

“While experimental studies can eg carefully control for potential confounders, these may have to be unpicked from observational studies, so in some ways the precision with which they can answer some questions may be limited. On the other hand, they can use very large samples in the “real world”, rather than in an artificial experimental setting; and the data they can be provided can be useful in answering a range of questions, not necessarily all of them thought of at the time the data are collected. While the precision of answers may be excellent or somewhat limited, this particular study uses very large datasets (nearly 50,000 swabs were collected); and it is one of a series of observations over time, which allows for comparison and analysis of how things are changing over time. This provides very powerful, valuable information.

“This study, published in the context of plans to relax the non-pharmaceutical interventions – the Covid restrictions or “lockdown” – provides answers to crucial questions about the amount of Covid-19 disease in the community, and how it is changing over time. The results are at once reassuring, and very alarming. They are reassuring inasmuch as they show that the morbidity and mortality caused by the SARS-CoV-2 has reduced, as vaccines have provided protection against infection, and (more so) against serious illness and death; and it confirms that vaccination protects people who have been vaccinated. However the rate of increase in infections that it reports is extremely worrying. The authors found that rates are increasing more than exponentially: the doubling time for case numbers has more than halved since the previous report, from about 15 days, to just over 6 days. Infections are increasing in all areas, particularly London. These findings are consistent with other studies, including those published by the Office for National Statistics.

“This report did not provide information on mitigating factors such as social distancing and other behaviours.

“On 05 July the Secretary of State for Health asked the rhetorical question about the relaxation of Covid-19 restrictions: “If not now, when?” This question suggests a fallacious binary: “it’s now or never”. Of course, the reality is more complicated. What are our goals in making the decision? And, for scientists, what will the consequences be of doing it now, or at some other point in time? And how might we decide when the optimum time would be?

“Part of the answer is blindingly obvious, particularly given the growing concerns about Long Covid. Case numbers are rising more than exponentially; and a significant proportion of the cases will have Long Covid with prolonged or permanent limitations. Even if a relatively small proportion of cases need hospital admission, critical care, or die, with extremely large numbers of cases, the numbers will be large, and services are already overwhelmed, exhausted, and struggling to catch up with a backlog of non-Covid cases. The sheer number of cases will be terrifying, suggesting that many people will have the good sense not to engage in the sort of economic activity that one imagines the politicians are hoping for.

“The answer many scientists would give to “when?”, would relate to the incidence (the number of cases arising per unit time), the absolute number of cases at that point in time, and the trajectory of case numbers. This paper tells us that we should not be relaxing restrictions right now, or until case numbers have fallen and are falling. If anything we should be tightening them and enforcing them more rigorously.

“And the paper will, in due course, provide some of the answers to the inevitable retrospective questions “how well did what we do work, and could we have done it better”.

“It seems very likely that this study, and others like it, will demonstrate the folly of the UK Government’s approach.”



‘REACT-1 round 13 interim report: acceleration of SARS-CoV-2 Delta epidemic in the community in England during late June and early July 2021’ by Steven Riley et al is a preprint embargoed until 00:01 Thursday 8 July.



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



Declared interests

None received.


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