Near the start of the COVID-19 pandemic, the World Health Organisation (WHO) identified diagnostic testing as one of the key factors in monitoring and managing the spread of the disease. Since then, many test forms have entered development, evaluation, and production globally. Currently, there are two main types of tests available for the detection of SARS-CoV-2: Lateral Flow Assay (LFA) tests and Polymerase Chain Reaction (PCR) testing. PCR is most commonly used for testing individuals that are already displaying symptoms, such as a fever, cough and/or loss of taste and smell. PCR tests must be processed in specialist laboratories, and are carried out by trained professionals, with results provided after several days.
On the other hand, LFA antigen tests offer a rapid, economic option for testing individuals that are not currently presenting with symptoms, or are asymptomatic, despite being highly infectious. It is estimated that around one third of people with coronavirus never show symptoms, meaning there is a large population of potentially infectious individuals who are not being PCR tested, and therefore not recorded as positive1. Identifying these cases through regular, rapid testing will help to implement quarantine sooner, preventing further spread of the disease – particularly important for routine testing in facilities such as schools, healthcare institutions and transport, as well as mass population testing.
Benefits of LFA testing
One key benefit of the LFA antigen test is its effectiveness to detect a high viral load: quantifying the viral antigen at its most infectious stage. Studies have shown that the more virus present in the nose and throat, the more infectious a person is. Consequently, assessing this viral load will enable faster identification and isolation of these highly infectious individuals, to ultimately minimise further transmission and reduce the R rate2.
Another benefit is that LFA tests are mobile and rapid, suitable for use at the point-of-care without the need for specialist equipment. In this format, the tests can be rapidly deployed across multiple locations without stringent infrastructure or training requirements.
In addition, LFA tests can provide much faster results than PCR tests, with most test displaying a result within 30 minutes. PCR test results can take several days from testing to results, leaving a window in which infection can spread. Rapid testing means a faster start to quarantine for infectious individuals, and so greater control over disease spread.
Applications of LFA testing
To-date, rapid diagnostic assays have identified 27,000 SARS-CoV-2-infected people in the UK who would not otherwise have known to self-isolate3. Though the sensitivity of LFA tests can be limited for less-infectious patients with low viral loads in comparison to PCR, the tests are highly effective at identifying the individuals that are most likely to further spread the disease who have higher viral loads4. In conjunction with PCR testing, LFA devices offer a more complete approach to diagnostics and increase the availability and speed of testing, whilst minimising the pressure on in-hospital laboratories.
Rapid tests also support testing in low- and middle-income countries, where resources and access to healthcare facilities may be limited. Avacta recently announced a partnership with Mologic to accelerate the CE marking of Avacta’s rapid antigen test, with support from Mologic’s international manufacturing partners including Global Access Diagnostics (GAD). GAD aims to provide testing access in areas where laboratory facilities and trained health care workers can be scarce resources.
The speed and ease of LFA tests, as well as their low cost of production, facilitates testing of large numbers of people. This, in conjunction with other infection control and testing methods, gives populations the greatest chance at preventing and controlling the spread of the disease.
Mass screening can help to aid decision and policy making by providing a larger amount of data on numbers and location of infectious individuals, as well as informing on case numbers. The more people that are tested, the more data can be captured to provide a more complete picture on the state of disease spread and R-number.
Another important application of LFA tests is the potential for home-based consumer testing. Since there is no need for specialist training to administer the test, and the visual results are easy to read, rapid test kits are ideal candidates for commercial sale, broadening the availability of testing even further.
Avacta’s Lateral Flow Testing Capabilities
At Avacta, we have dedicated our diagnostics unit to developing technology for the fight against COVID-19. Our Affimer® technology has been implemented in a number of test forms, including our AffiDX® LFA test.
In February, 2021, we announced the results of the initial evaluation of the AffiDX® SARS-CoV-2 antigen lateral flow test, which used clinical samples in Europe and the UK. The data from these studies demonstrated excellent performance in identifying patients with an infectious viral load, and no false positives.
Following this encouraging data, the test progressed to full clinical validation with a larger number of patient samples. In April, the data demonstrated excellent performance across a broad range of viral loads; 98% clinical sensitivity and 99% clinical specificity. Critically, in patients with a high viral load and at their most infectious, the sensitivity rose to 100%.
These robust results complete the technical data set for self-declaration of a CE mark, allowing for professional use of the tests. With the CE marked product registered in Europe we are pleased to be able to launch the test commercially across Europe, to contribute to increased testing capabilities, whilst tackling the virus’ asymptomatic spread, for earlier quarantine and treatment.
In June, Avacta announced that the AffiDX® SARS-CoV-2 antigen lateral flow test detects the Delta variant. The test is routinely monitored against emerging variants.
Beyond Coronavirus
LFA diagnostic tests will undoubtedly play an important role against future diseases and to help stop local outbreaks spreading nationally and globally. Prior to the ongoing pandemic, LFA had already proved valuable in testing against other disease outbreaks including Zika, Ebola and Malaria5,6,7. In fact, a report by the WHO in 2017 found that 2.7 billion rapid tests for Malaria were sold in 2010 -2019, with nearly 80% of these sales to sub-Saharan Africa7.
We have already seen the united response to the SARS-CoV-2 outbreak, with institutions globally working to provide technology to fight the pandemic. Although challenging, this has provided healthcare systems with a strong basis to work from when identifying and responding to future outbreaks.
Sources
- https://pubmed.ncbi.nlm.nih.gov/33481642/
- https://www.ox.ac.uk/news/2021-01-21-lateral-flow-devices-detect-most-infectious-covid-19-cases-and-could-allow-safer
- Covid-19: Scientists challenge ‘flawed’ lateral flow tests report – BBC News
- Asymptomatic testing for SARS-CoV-2 using antigen-detecting lateral flow devices. Evidence from performance data October 2020 – May 2021. Department of Health & Social Care (2021). Available online: https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/999866/asymptomatic-testing-for-SARS-CoV-2-using-antigen-detecting-lateral-flow-devices-evidence-from-performance-data-Oct-2020-to-May-2021.pdf
- https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5780406/
- https://pubmed.ncbi.nlm.nih.gov/30845203/
- Global Malaria Program. Rapid diagnostics tests. World Health Organization (WHO) (2021). Available online: https://www.who.int/teams/global-malaria-programme/case-management/diagnosis/rapid-diagnostic-tests