Testing for COVID-19 infection and for immunity

Robin Cordell, Board Director, Council for Work and Health


Why is testing useful and what types of test are there?

Testing for COVID-19 is likely to significantly enhance risk assessment and management:

There are two types of tests.

  • The Antigen test, a laboratory test, looks directly for the virus’s genetic material (RNA) through a process termed polymerase chain reaction (PCR).
  • Antibody tests are currently being evaluated, which look for evidence that the person has been exposed and has immune antibodies to the virus.

Antigen testing

Testing for presence of the coronavirus (the antigen test) in those self-isolating at home with symptoms has now been extended to all essential workers (as defined at: https://www.gov.uk/government/news/coronavirus-testing-extended-to-all-essential-workers-in-england-who-have-symptoms).

Eligible workers (or their household contacts with symptoms) include:

  • all NHS and social care staff, including hospital, community and primary care, and staff providing support to frontline NHS services (for example accommodation, catering) and voluntary workers
  • police, fire and rescue services
  • local authority staff, including frontline benefits workers and those working with vulnerable children and adults, victims of domestic abuse, and those working with the homeless and rough sleepers
  • defence, prisons and probation staff, and judiciary
  • other frontline workers as determined locally or nationally, including critical personnel in the continuity of energy, utilities and waste networks, and workers critical to the continuity of essential movement of goods

Those eligible and with symptoms of a high temperature or new continuous cough and would like to be tested for the virus should speak to their employer.  The process for getting tested is at: https://www.gov.uk/guidance/coronavirus-covid-19-getting-tested.

As well as regional testing sites, where most people will have appointments, and increasing numbers of home testing kits, 100 mobile units run by the Armed Forces are now available for essential workers who work in more vulnerable settings, as at: https://www.gov.uk/government/news/mobile-coronavirus-testing-units-to-target-frontline-workers

A note of caution – no test is 100% reliable

Testing for presence of the virus will make a significant contribution to risk assessment. It is considered that sensitivity (picking up the presence of the virus) of the PCR antigen test is at most 90%. This means though that of 100 people tested who actually have the virus, at least 10 will test negative; a false negative.  Therefore having a negative test does not necessarily mean the individual does not have the virus, and is safe to go back to work.

We recommended that employees be asked to contact the occupational health provider as soon as they have the test result, whether this is positive or negative for the virus.

An occupational health clinician can then call to help the employee in their return to work, depending on the test results and any symptoms they still have.  Following this they can be certified as fit to return to work, or not fit pending further occupational health review if this is needed.  It is possible some people will need to be tested again.

Antibody testing (for immunity to the virus)

The antibody test is a blood sample (finger prick) applied to a reagent strip with immediate result and is being manufactured in high volume. This device is expected to be suitable for wider community use, once reliability is confirmed.

The Government’s specification for antibody devices is to accurately and reliably measure the presence of IgG (longer term response) antibodies to the virus, indicating infection at least 2 to 3 weeks earlier. Some devices also measure IgM (immediate immune response) antibodies, present for up to 3 weeks after infection.

At present there are no antibody tests sufficiently reliable to safely inform decisions on risk assessment. Development of these tests is a key element (Pillar 3) of the Government’s strategy at: https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/878121/coronavirus-covid-19-testing-strategy.pdf.

Testing strategy and plan for your organisation

We suggest teleconference meetings between clients in sectors prioritised for testing and occupational health to discuss how this may be implemented in their organisation.

This will be to consider how antigen testing will be done for essential workers and/or their household contacts with symptoms (within the first three days of onset), in accordance with Government policy, and for all clients, how antibody tests will be accessed and the results used in future, once those shown to be at least 98% reliable are available.

Dr Robin Cordell, Director, Council for Work and Health