Allyson Pollock: Testing, testing…for SARS-CoV-2 in asymptomatic people

Ahead of the next covid-19 known unknowns webinar, Allyson Pollock discusses the uncertainties around testing for SARS-CoV-2 in asymptomatic people

The topic of our next The BMJ/MRC Integrative Epidemiology Unit covid-19 webinar is testing for SARS-CoV-2 in asymptomatic people. It continues the theme of our previous webinars, which have looked at public health interventions that have been rolled out without adequate evaluation of the data—either data that are already available or data which are being collected during the rollout. Mass testing—and mass testing of asymptomatic people in particular—in schools, universities, care homes, hospitals, prisons, communities, and workplaces is close to an evidence-free zone. While many countries agencies (e.g. Germany’s Robert Koch Institute, or the European Centre for Disease Prevention & Control), and the UK’s SAGE committee, advise that the focus of effort and resources should be on identifying symptomatic people and their contacts, the UK government sees mass testing simply as another “world-beating” initiative. [1,2]

Finding and diagnosing symptomatic people, tracing their contacts, and isolating cases and contacts are the classic tools of communicable disease control. Sounds simple? In practice, each of these little steps is a complex task involving multiple organisations and different types of professionals. Miss a step and you miss the opportunity to break the chains of infection and transmission. Our success rate isn’t good. Almost a year into the covid-19 pandemic, the effectiveness of the UK’s contact tracing, the key intervention for breaking the chain of transmission, has still not been evaluated; fewer than 20% of people isolate, with financial constraints and caring responsibilities the main impediments to compliance. [3] According to media reports an estimated £22bn has been spent so far on test and trace for symptomatic people for which the benefits are still uncertain.  

When it comes to testing for covid-19, the fundamental tenets of public health have been set aside. Community testing has been divorced from health services, bypassing GPs, NHS labs, and public health departments. [4] Instead of rebuilding capacity in the public system, the government has funded a hugely expensive parallel edifice of fragmented private providers, with no previous experience. For over eight months, GPs were denied access to tests and results for their patients. [5] The tests themselves are being used outside their prescribed purpose, and manufacturers’ instructions, namely, “clinical correlation with patient history and other diagnostic information is necessary to determine infection status” are ignored. [6]

In August 2020, Tony Blair’s Institute for Global Change felt sufficiently confident to issue two reports advocating mass testing and credentialling—no test, no travel, no work, no play. [7] Jeremy Hunt, one of the report’s co-signatories and current chair of the Health Select Committee, has been an enthusiastic supporter of mass testing, and the Health Select Committee has thus far failed to address the lack of evidence in support of mass testing.

In September 2020, leaked government documents revealed the scale of planned expenditure on mass testing to be £100bn, almost 70% of the NHS annual budget for England in 2019. Hundreds of millions of tests have been purchased so far, prior to evaluations in field settings. 

While there’s an understandable desire to move fast, pandemic preparedness should have ensured systems were in place to ensure robust procurement and allow for some form of evaluation.

“The true test of intelligence is not how much we know how to do, but how we behave when we don’t know what to do.” [8] The billions of pounds spent on contracts for tests without formal tender and bypassing tendering procedures reveals that thus far commercial interests have trumped the public health concerns. 

Communicable disease know-how built up over a century and more has been ignored. Experts in public health and communicable disease control and on the UK National Screening Committee have been sidelined, and replaced by captains of industry, most notably the appointment of Dido Harding and outsourcing of testing and tracing to Serco, Deloitte, and Amazon.

The long established rules and standards for scientific evaluation have not been followed. And nowhere is this more evident than in the reporting of UK test and trace data on cases. These make no distinction between people who are asymptomatic, presymptomatic, paucisymptomatic, and symptomatic, or whether infectious or not. A case is simply a positive test, regardless of symptoms and purpose of testing. And yet a case definition is key to evaluating the effectiveness of screening, contact tracing, and estimating secondary attack rates. [9] To add to the confusion and blur, since 27 January 2021 people testing positive with lateral flow tests (LFTs) are counted as cases under track and trace, and confirmatory PCR is no longer required. [10]

Since 10 January mass testing using LFTs has been ramped up across local authorities such that LFTs now number approximately 350,000 tests or more each day, outnumbering PCR tests. [11,12]

Given that “all screening programmes do harm; some do good as well, and, of these, some do more good than harm at reasonable cost.” [13] It is crucial to address the question as to whether mass testing of healthy people is cost effective—not least given the scale of spending.

The uncertainties generated by the failure to follow the fundamental principles and establish the purpose of testing programmes including costs, benefits, and harms has created space for division. To paraphrase George Bernard Shaw, the test of good science and evidence is seeing how people behave in a quarrel.

Until we subject mass testing programmes and other non pharmaceutical interventions to rigorous evaluation in the way we are required to do for medicines or vaccines, disputes over whether LFTs are more sensitive and more likely to detect infectious people than PCR tests, and the effectiveness of test and trace (including whether screening asymptomatic people is more effective than test and trace for symptomatic people at breaking chains of transmission ) are unsubstantiated—leaving us in the realm of unknowns. [14]

Details of the content and free registration for the next covid webinar is here. The next webinar will be about covid-19 testing in asymptomatic people #covidunknowns on 11 February 2021, 16:00-18:00.

Allyson M Pollock, Professor in Public Health, Population Health Sciences Institute, Faculty of Medical Sciences, Newcastle University, Newcastle, UK

Competing interests: AP was a member of Independent SAGE. 


    1. Robert Koch Institut. Notes on testing patients for infection with the novel coronavirus SARS-CoV-2 [Hinweise zur Testung von Patienten auf Infektion mit dem neuartigen Coronavirus SARS-CoV-2] 25 Jan 21
    2. European Centre for Disease Prevention and Control. Options for the use of rapid antigen tests for COVID-19 in the EU/EEA and the UK. 19 November 2020.
    3. Smith LE, Potts HWW, Amlot R, Fear NT, Michie S, Rubin J. Adherence to the test, trace and isolate system: results from a time series of 21 nationally representative surveys in the UK (the COVID-19 Rapid Survey of Adherence to Interventions and Responses [CORSAIR] study). medRxiv 2020: 2020.09.15.20191957.
    4. Roderick P, Pollock AM, Macfarlane A. Getting back on track: control of covid-19 outbreaks in the community. BMJ 2020;369:m2484.
    5. Harding-Edgar L, McCartney M, Pollock AM. Test and trace strategy has overlooked importance of clinical input, clinical oversight and integration. JRSM 28 Oct 2020. 10.1136/bmj.m1465
    6. Innova Medical Group Inc. SARS-CoV-2 antigen rapid qualitative test instructions for use. 01 Jul 2020.
    7. Taking the UK’s testing strategy to the next level. Tony Blair Institute for Global Change 17 Aug 2020.
    8. Holt J. How children fail. Pitman 1964.
    9. Qiu X, Nergiz AI, Maraolo AE, Bogoch II, Low N, Cevik M. Defining the role of asymptomatic and pre-symptomatic SARS-CoV-2 transmission – a living systematic review. Clin Microbiol Infect. 2021 Jan 20:S1198-743X(21)00038-0.
    10. Weekly statistics for NHS Test and Trace (England): 21 January to 27 January 2021. GOV.UK 2021 Feb 04.
    11. Asymptomatic testing to be rolled out across the country starting this week. GOV.UK 2021 Jan 10.
    12. Testing in England. Coronavirus in the UK. GOV.UK. JAM, Patnick J, Blanks RG. Maximising benefit and minimising harm of screening. BMJ 2001;336(7642):480–483.
    13. Crozier A, Rajan S, Buchan I, McKee M. Put to the test: use of rapid testing technologies for covid-19. BMJ 2021 Feb 03;372:n208