Rapid antigen test

A rapid antigen test (RAT), or rapid test, is a rapid diagnostic test suitable for point-of-care testing that directly detects the presence or absence of an antigen. It is commonly used for the detection of SARS-CoV-2, the virus that causes COVID-19. Rapid tests are a type of lateral flow tests that detect protein, distinguishing it from other medical tests that detect antibodies (antibody tests) or nucleic acid (nucleic acid tests), of either laboratory or point-of-care types. Rapid tests generally give a result in 5 to 30 minutes, require minimal training or infrastructure, and have significant cost advantages.

Rapid antigen test
SARS-CoV-2 rapid tests. Viral antigen detection lateral flow tests
SynonymsRapid antigen detection test (RADT), lateral flow test, lateral flow device, rapid test
PurposeTo diagnose infections

Uses of Rapid Antigen tests

Common examples of RATs or RADTs include:

Scientific basis and underlying biology

Antigen tests and antibody tests are often immunoassays (IAs) of one kind or another, such as dipstick IAs or fluorescence immunoassays, however RAT is an immunochromatographic assay which gives visual results that can be seen with the naked eye. It is considered to be qualitative but a person experienced in RDT testing can easily quantify the results. Being a screening test, if the sensitivity and specificity are relatively low for the test then the results should be evaluated on the basis of confirmatory tests like PCR testing or western blot.

One inherent advantage of an antigen test over an antibody test (such as antibody-detecting rapid HIV tests) is that it can take time for the immune system to develop antibodies after infection begins, but the foreign antigen is present right away. Although any diagnostic test may have false negatives, this latency period can open an especially wide avenue for false negatives in antibody tests, although the particulars depend on which disease and which test are involved. A rapid antigen tests typically cost around US$5.00 to manufacture.

COVID-19 rapid antigen tests/rapid tests

Rapid antigen tests for COVID-19 are one of the most useful application of these tests. Often called lateral flow tests, they have provided global governments with several benefits. They are quick to implement with minimal training, offered significant cost advantages, costing a fraction of existing forms of PCR testing and give users a result within 5–30 minutes. Rapid antigen tests have found their best use as part of mass testing or population-wide screening approaches. They are successful in these approaches because in addition to the aforementioned benefits, they identify individuals who are the most infectious and could potentially spread the virus to a large number of other people. This differs slightly from other forms of COVID-19 such as PCR that are generally seen to be a useful test for individuals.

History of COVID-19 rapid test technology development

Rapid tests for COVID-19 emerged from major investment by the United Kingdom's controversial Moonshot program, a £100 billion program to systematically assess, develop and implement new technologies for COVID-19 testing.[2] Rapid tests initially sat within this systematic evaluation pipeline alongside many other putative COVID-19 testing technologies like Lamp, Lampore, point of care PCR, mass spectrometry and sample pooling. However, as evaluations continued, rapid tests emerged as the most successful form of COVID-19 testing within this program to complement existing PCR testing.

International guidance for COVID-19 rapid test technology use and development

The early scientific rationale for the potential utility of Rapid tests and global direction for rapid test technology development was boosted by interim guidance from the World Health Organisation (WHO) that flagged the potential benefits. The report noted that Rapid tests were much easier to implement, had cost benefits. The WHO recommended their use in outbreaks, for early identification of cases and to monitor disease trends. Later, and subsequent to a rapidly increasing body of studies, this recommendation was expanded by the European Commission. The European Commission recommended the use of rapid test technology for population-wide screening where the proportion of test positivity is high or very high . By January 2021, the European Commission agreed to strengthen their position, advocating much greater use of Rapid tests, noting that "should research prove that rapid antigen tests can be conducted by the testee themselves.... self-testing with or without professional guidance could also be considered."

Initial studies

One of the definitive studies for rapid tests was completed by Public Health England, University of Oxford and University of Manchester and launched by Professor Richard Body and Dr Lennard Lee. The Falcon-C19 study which was launched within three days on the 17th of September. The first patient was recruited at the Manchester City Ethiad stadium carpark at a new COVID-19 testing research centre. The study rapidly extended to include 14 community research sites across the United Kingdom. The study closed on the 23rd of October, having completed 878 individuals. The study was one of the fastest recruiting UK COVID-19 research studies in the country. The study provided definitive evidence that rapid test devices were able to pick up positive results with high accuracy. A total of 4 rapid test, including Innova and Orientgene were validated in this study using swab samples from individuals with symptomatic and asymptomatic disease.[3]

Around the release of the interim analysis of this UK study, the United States confirmed that 100 million rapid tests would be purchased from Abbott and shipping to across the country to start similar US studies to complement the University of Oxford initiated studies.[4]

Valuation studies across the world

On the 2nd of November, Slovakia became the first country in the world to instigate country-wide mass testing using rapid tests. 5 million rapid tests were performed by 60,000 staff who utilised the SD Biosensor antigen test and performed swabbing on the population. This mass testing approach reduced the prevalence of COVID-19 by 60%.[5][6] This then lead to the pan-European recommendation that Rapid tests were used as part of population-wide screening .

The United Kingdom continued their ongoing rapid test development program using the Innova rapid test, with increasing urgency as COVID-19 cases increased across Europe. On the 6th of November, the Prime Minister, Boris Johnson started city-wide screening of Liverpool as part of the accelerated technology evaluation.[7] Further expansion of rapid tests pilots were also launched for many sectors where testing had not been previously available. These included students at Universities who had been particularly hit by outbreaks. This initially started at Durham University who had the infrastructure and expertise to manage the Rapid test program,[8] but was expanded the majority of UK Universities and enabled the national evacuation-style plan to get students safely home for Christmas.[9] Rapid tests were also implemented within the National Health Service for staff to reduce possible transmission to patients,[10] local authorities [11][12] and Care homes to enable visits to visit residents.[13][14] On the 18th of November, Wales completed the first whole borough testing at a Merthyr Tydfil.[15][16] At this time, testing was also implemented across schools in the United States for students with symptoms [17] and across Portuguese care homes and schools.[18]

Global efforts to step up evaluations of rapid tests were initiated by the World Health organisation Emergencies Department who launched a major Rapid diagnostic test implementation project on the 10th of November, aided by agreement from the Bill and Melinda Gates foundation that limited costs for Low and middle-income countries.[19][20]

Austria started country-wide mass testing on the 5th of December and ordered seven million tests consisting of the SD Biosensor test and Siemens Clinitest (aka Orientgene).[21][22]

By the middle of December, there were many studies confirming the efficacy and success of using rapid tests to identify individuals with COVID-19 including studies in the Netherlands,[23] the United Kingdom,[24] and the United States of America.[25] These studies all enabled rapid tests to enter standard national COVID-19 testing strategies. Global piloting of rapid tests was now common place in schools in Canada,[26] travel hubs in Indonesia,[27] and across India.[28]

Concerns about use/Controversies.

Many individuals have raised concerns that the accuracy of rapid tests were not as good as the existing form of COVID-19 testing PCR. Data released from the United Kingdom's City-wide screen in Liverpool illustrated that army operators of the test did obtain the test performance of trained laboratory scientists [29] and also following other pilots in India.[30] This caused minor issues within the scientific community where there was a debate about whether Rapid tests might lead to false reassurance and a change in behaviour. However, a shift in thinking about the use of Rapid tests was confirmed following a publication from the United States. Professor Michael Mina theorised that Rapid Tests would still be useful as it identified infectious individuals [31] and potential benefits observed from repeating rapid test and getting a result much quicker than other forms of testing.[32] The United Kingdom's chief clinical, Dr Susan Hopkins also noted that Rapid tests provided a means to “test finds people that doesn't we couldn't otherwise find”.[33]

Noting the ability to identify cases more rapidly, and considering the ensuing escalation in cases in Europe, the European commission met on the 11th of December and developed a common European framework for “use, validation and mutual recognition of rapid tests”, committing 100 million euros for the purchase of tests from Roche and Abbott. Stella Kyriakides, commissioner for Health and Food Safety said ““Rapid antigen tests offer us speed, reliability and quick responses to isolate COVID cases. This is crucial to slow down the spread of the pandemic”. [34]

Other individuals have raised concerns about the slow uptake and deployment of rapid tests and potential loss of life that might have occurred as a result. An academic group from Canada noted that half the deaths in care homes in the early part of the pandemic could have been prevented with rapid tests. . This was summed up by a controversial cartoon depiction released by a "Rapid Test & Trace", a Canadian Rapid Test advocacy group, that depicted a long term care home on fire, people asking for help, but the firemen debating whether to use a hose with 150 psi or wait for several hours.

Global regulatory approval for use for COVID-19 testing

Following the success of numerous studies across the world to analyse rapid tests from August 2020, Rapid tests were approved by regulatory bodies across the world as part of a strategy to use testing as “a new approach to combat the pandemic”. On the 16th of December, the FDA became the first authority to approve the Abbott rapid test.[35] Subsequent approvals were given for the Ellume COVID-19 home test.[36]

Rapid tests were also approved by Health Canada with their advisor, Professor David Juncter noting “the best rapid tests are highly accurate at detecting contagious individuals“ and Infectious disease specialist Jean Longtin noting "It will allow us to move faster than the virus and find the person's contacts in an hour or two, instead of waiting 24 hours".[37][38]

The United Kingdom's MHRA confirmed their approval of the Innova rapid test for self-use testing on the 23rd of December. Following the clear global success of this global development of rapid tests, Sir John Bell, Regius professor of medicine at the University of Oxford said “Rapid tests were a central bit of good defence against coronavirus because they were fast, cheap and available for repeat use”.[39]

Rapid tests as a "return to normal"

Spain became the first country to use Rapid tests to facilitate a return-to-normal with Rapid tests being widely available in pharmacies,[40] and a free music concert held in Barcelona to individuals who took a rapid test.[41] A similar approach was taken in Albania to enable music festivals.[42] However, many experts were unsure of this approach believing that “rapid tests are not the solution to restart normal life” [43] but might be used in combination with other vital infection prevention control measures such as wearing appropriate PPE, washing hands regularly and social distancing to allow people to have that vital time with those they love while helping to keep them safer.[44]

New COVID-19 strains

On the 22nd of December 2020, a new more infectious strain of SARS-CoV-2 was identified in the United Kingdom, VOC-202012/01. The strain rapidly spread across the world. With widespread global use of this form of COVID-19 testing, there was a concern that this variant would render rapid testing obsolete. As part of the UK's accelerated technology evaluation of lateral flow, within 24 hours, Public Health England laboratories were able to confirm rapid test in global development were not affected and they could identify the new variant. This was because rapid test generally targets the nucleocapsid protein and not the spike protein.[45]

Humanitarian uses for rapid tests

In addition to routine community use, rapid tests have also been utilised as part of humanitarian efforts during the pandemic. Following the flooding in Jakarta in Indonesia on the 2nd of December, Rapid tests were made available in flood shelters.[46] Furthermore, following the closure of national borders in Europe following the emergency of the new UK strain just before Christmas, nearly 6,000 lorry drivers were stranded without food.,[47] effectively stopping Christmas food deliveries. Rapid tests were deployed by French firefighters within 24 hours at the UK-French border. Rapid tests enabled lorries to get on the road and complete their deliveries and return to their families for Christmas, demonstrating the potential global utility of having an easily implementable COVID-19 test.[48][49] Médecins Sans Frontières/Doctors Without Borders strongly endorsed the use of rapid tests in lower and middle income countries noting "COVID-19 antigen tests can deliver rapid and actionable results, ensuring timely identification of people infected with the virus at the community level".

United States of America and rapid tests

Having initially invested considerably in rapid test technology development along with the United Kingdom, further evaluation of rapid tests as part of mass testing approaches in the United States of American stalled as a result of the impasse around the $900 billion in COVID-19 relief contained within the 2020 Consolidated Appropriations Act, 2021. The bill was criticised for not specifically ring-fencing investment in rapid tests as a cost-economical and effective form of population-wide testing. . Scientists in the United States, such as Professor Michael Mina (Harvard University) noted that tests were a “very powerful adjunct to everything else that people are already doing” and "home tests for COVID-19 Could Slash Infection Rate" . This view was reinforced by Professor William A. Haseltine (Harvard University) in an article in Forbes magazine proposing "rapid, self-administered testing could stem the ever-surging tide of disease and death" and an article by Professor Annie Sparrow (Mount Sinai, New York) proposing "Cheap Mass Testing is Vital for Pandemic Victory" in view of "the emergency of the highly contagious and fast-spreading B117 strain in the UK, and a similar strain from South Africa". Nevertheless, rapid home tests for COVID-19 were publicly available to individuals in January 2020 following the earlier FDA approval . These tests were reimbursed by US health insurance for people with covid-19 symptoms, or those who have had close contact with an infected person or with someone showing symptoms. An article in the Washington Post proposed that the maximum benefit of rapid tests in the United States of America might not be realised until "federal government covered testing for asymptomatic people because transmission by those people is such a huge part of the outbreak" as testing these individuals was not covered by health insurance. Following the election of a new president in January 2021, the United States began to restart investing in rapid test technology development with the publication of The Biden-Harris and associated presidential executive orders.

Global market value

Following the widespread utilisation of rapid tests across the world, rapid tests have a market value of 15,000 million dollars, however, the market is expected to cease from 2024 due to the vaccination of global population by the end of 2023.[50] In the United States of America, the market for rapid tests was US$3.9 billion with a >20% growth rate in hospitals, clinics, Asia Pacific but also as end-user tests.[51] International market analysts have forecasted that manufacturers of rapid tests will face ongoing increasing demands as more individuals and countries start to use rapid tests to identify individuals with milder symptoms.[52] A number of commentators and scientists from the United States had raised concerns whether the global manufacturing network were able to meet global demand and manufacture the hundreds of millions of tests that would be needed for frequent rapid testing.[53][54]

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