There are two key reasons for testing individuals. The first is to understand whether someone currently has the virus (antigen test), the second whether someone has had the virus in the past (antibody test). Both are important for the individual, but beyond that the results of these tests at population level can help inform and direct the wider policy and health service response to the virus.
The PCR test: who’s got the virus?
The main test currently being used to identify who has the virus is a type of antigen test called a PCR (polymerase chain reaction) test. This involves taking a swab from an individual’s nose or throat, and then sending the swab to a laboratory to be analysed.
The results of these tests are being used to:
- enable appropriate clinical management of patients
- identify infected individuals who need to self-isolate and, where appropriate, facilitate contact tracing and containment at a population level
- inform policy decisions for implementing, continuing or easing lockdown.
At population level, this test was used to try to contain cases of the virus in the initial early stages of the outbreak when an individual testing positive was isolated, their contacts traced and tested (and isolated if required). After lockdown measures are eased, this approach could help contain further, localised, outbreaks.
Testing is also being used to understand the extent to which the virus is circulating in the community through random community testing (patients of 100 general practices in England are being tested for this purpose). In some countries, such as South Korea, the PCR test has been used in combination with phone apps, to aid contact tracing, identification and risk management for patients. This is part of the UK government strategy (see below).
The antibody test: who’s had the virus?
The antibody test indicates whether someone has had the virus in the past, three to four weeks after they exhibited symptoms. This test picks up the presence of antibodies that the body develops to fight the virus, rather than the presence of the virus itself. It is also hoped that this test will help indicate possible immunity (although it is too early to tell what level of immunity having antibodies confers).
At the end of April there were no antibody tests being carried out in the UK as part of a government strategy; the government has not yet completed its assessment of the many candidate tests. It is essential that these tests are accurate, so that individuals and their contacts are not put at risk by a ‘false positive’ test result, ie, an inaccurate result that suggests they have had the virus when they have not. This risk applies to all but a ‘false positive’ result would be particularly risky for those working in the NHS and social care, other key workers and those in contact with highly vulnerable groups, who may believe they are safe to work.
When an accurate test is found, it will have several uses (depending on the extent to which antibodies confer immunity). Identifying people who have had the virus could:
- allow some key workers to return to work
- allow family, friends and others to be confident about contact with shielded individuals (where appropriate)
- let individuals know whether they have had the virus
- at population level, indicate the proportion of the population locally and nationally that has had the virus which could inform future policy decisions (eg, easing restrictions and prioritising people for future vaccination).
It is hoped that these tests will be easily administered (e.g., a self-administered finger-prick test), quick (a result within 15-30 minutes) and able to be done within the home. This would mean potentially millions of people would know whether they had had the virus, subject to the volume of tests available. This knowledge will also allow much more accurate and targeted planning in response to the virus in local areas over time, as well as allowing more precision around outcomes, such as mortality rates.
Where are we now?
Testing has been, and will continue to be, an important part of the government’s strategy for tackling Covid-19 and planning the recovery from it. Knowing who has the virus, and expanding testing more widely across the population as capacity grows, helps to provide appropriate care for individuals, understand the speed and extent of spread in populations, and therefore the capacity and policies needed to respond (eg, how and when to ease lockdown). Knowing who has had the virus indicates how far the virus has spread through the population, who is at higher or lower risk from the virus, helps assess future risk, eg, how likely further outbreaks may be and the appropriate response to them, and informs future policy decisions.
The Department of Health and Social Care published its testing strategy Coronavirus (Covid-19): scaling up our testing programmes on 4 April, setting out what it intended to do across ‘five pillars’.
- Pillar 1 is NHS swab (PCR) testing for those with a medical need and critical key workers. The government met its aim of 10,000 tests per day by the end of March and committed to 25,000 per day by the end of April. This pillar was designed to ensure that public sector lab capacity was used for those with highest medical need in hospital and capacity expanded.
- Pillar 2 is the development of partnerships with businesses who can develop and deliver commercial swab (PCR) testing to enable greater capacity to test more critical key workers in the NHS, but also key workers in social care and other sectors. The service was launched at the beginning of April and expanded rapidly throughout the month.
Action under Pillars 1 and 2 has seen capacity for PCR testing increase. Increased capacity has meant that eligibility for testing has been sequentially widened over time to include: care home residents, social care staff and their families; key workers and their families (who can self-refer for a home-based postal or a mobile site test, if they are exhibiting symptoms and self-isolating); increased testing for care homes residents and staff, police stations and prisons across the UK in areas of high demand (provided by UK military personnel in mobile testing centres); and, at the end of April, all those in care homes or the NHS whether they have symptoms or not, all those over 65 (and their households) with symptoms, all workers (and their households) who have to leave home to work.
The increase in PCR testing paves the way for the re-introduction of testing and contact tracing among the wider population as part of the next phase of managing the virus. This is discussed further below.
- Pillar 3 is the development of antibody testing to identify who has had the virus, giving people knowledge and reducing their uncertainty. Antibody testing may also give an indication of possible immunity to the virus (although the science on this is not yet clear) and help inform, in the longer term, the use of social distancing measures and other policies. The government is working with companies to develop the reliable antibody tests needed before this work can roll-out.
- Pillar 4 is surveillance testing (testing in random samples of the population). This is essential to understand the rate of infection in the wider population, and how the virus is spreading across the UK. This testing helps to assess the impact of measures taken to contain the virus, to inform current and future actions, and to develop new tests and treatments. Population samples are being tested around the UK to understand how many people have had the virus to inform policy choices. At the beginning of April the first 800 samples were being analysed, with around 5,000 per week expected possible by the end of April.
- Finally, Pillar 5 involves building ‘a British diagnostics industry at scale’ to increase mass diagnostic testing to ensure everyone who needs either type of test can get one.
In the foreword to the strategy, Matt Hancock, the Secretary of State for Health and Social Care, set ‘the challenge across all five pillars, of 100,000 tests per day, by the end of April’, while First Secretary of State, Dominic Raab, confirmed during Prime Minister’s Questions that the next target was 250,000 a day, by an unspecified date.
On 17 April, Matt Hancock told the House of Commons Health Select Committee that the UK would start testing and contact tracing again, in conjunction with the use of a mobile phone app to support ‘digital contact tracing’ (tracking via mobile phone technology where and when someone has been in close contact with someone who has tested positive for Covid-19). This approach will only be feasible when the virus is broadly under control and at a relatively low level, and could ensure a quick response to localised outbreaks, treatment and, through tracing and self-isolation of contacts, controlling further spread. The government plans to start this renewed community contact tracing alongside the mobile app in mid-May, mobilising 18,000 contact tracers including 3,000 health professionals.
Testing and appropriate action on the results of tests are critical to keeping people safe, understanding this pandemic, and bringing and keeping it under control. Coverage and volume of testing has increased, and efforts continue to develop and procure an antibody test.
However, the current testing strategy (including how it compares with other countries) needs to be constantly scrutinised so it can be adapted if necessary, and lessons learnt during this pandemic can guide future responses to this and future epidemics and pandemics. Important questions for care consideration include the following.
- What was the impact of the UK’s approach to testing, contact tracing and quarantine in the early stages of the Covid-19 outbreak?
- Is the approach to expanding coverage and eligibility for testing for who has the virus appropriate?
- Is the volume of testing sufficient overall and is capacity increasing fast enough?
- Is the government receiving the right balance of scientific advice at the right time on the operational aspects and logistics of testing and subsequent actions, such as contact tracing, as well as the modelling?
- Is the approach to developing and procuring an antibody test appropriate?
- How does policy and practice of testing differ across the nations, regions and local areas of the UK and what can we learn from this?
- How are regions and local authorities being involved given, for example, their knowledge of local communities, role in local planning, and employment of and access to large numbers of people with the skills to help with logistical tasks such as contact tracing (eg, environmental health, sexual health and community infection control teams)?
Appropriate and agile testing is a core part of the response to any epidemic and the government’s approach will need to continue to develop over time in response to learning, scrutiny, the turn of events and learning from international experience.