Rapid antigen tests

25-11-2020

The PCR (polymerase chain reaction) tests are an important, but no longer the only component of the new testing strategy. For several weeks now, the European market has been flooded with dozens of commercially available rapid antigen tests, the reliability of which has not always been adequately tested.

The various authorities in our country have now purchased large quantities of rapid tests, in accordance with criteria put forward by the FAMHP and validated by the Task Force Testing.

A Task Force Testing was set up within the Government Commission for Coronavirus in October, together with a permanent Risk Assessment Group (RAG) Working Group Testing. This Task Force Testing was set up by the Interministerial Conference on Public Health and is made up of representatives of all authorities, including those of the federated entities, which means that this is also a consultative body whose objective is to achieve a coherent, integrated and flexible testing policy that is at the service of our population. Federated entities will set certain priorities with regard to the use of saliva or the rapid antigen tests and this will provide valuable information for the possible further roll-out of this strategy in other regions of our country. It is indeed the intention that the testing strategy will be continually adjusted, according to the results of the pilot projects and the latest scientific insights.

Based on the test indications and on the recommendations of this RAG Working Group, as published by Sciensano, and on the availability of the rapid antigen tests, the Task Force Testing has developed a summary diagram (see Appendix).

The broad lines of summary diagram are as follows:

The PCR test remains the gold standard and is used as a means of providing the most conclusive diagnosis possible and of proving a COVID-19 infection in all target groups.
In patients with symptoms (symptomatic patients), rapid antigen tests are almost as reliable as the PCR test. Rapid antigen tests must be performed within the first 5 days after the onset of symptoms, otherwise their sensitivity decreases significantly (risk of false negatives). The sensitivity of rapid tests also depends to a large extent on the quality of the sampling. They must therefore be carried out by trained personnel and in an adequate environment that guarantees everyone’s safety. If COVID-19 is strongly suspected and a rapid test was negative, or in the case of vulnerable persons experiencing symptoms of COVID-19, a PCR test must be requested.
In persons without symptoms (pre-symptomatic or asymptomatic patients), a limited number of studies have shown that rapid antigen tests are significantly less reliable than the PCR test. In the pre-symptomatic phase (the period before symptoms occur), rapid tests are not reliable. Rapid tests are reliable in people who remain asymptomatic with a high viral load, and who are therefore contagious. For that reason, the use of rapid tests on persons who are asymptomatic will be restricted for the time being to settings in which a high prevalence can be expected, such as in a cluster in group settings with a low risk profile (not, therefore, in locations such as residential care centres). In this context, the current guidelines will continue to apply for the detection and quarantining of high-risk contacts, but antigen tests can be used to carry out a broader investigation of the cluster.
Saliva samples are promising in the case of repeated testing because saliva can be taken by the individuals themselves (without the intervention of healthcare personnel or the use of protective equipment) and because that method is more child friendly. However, a PCR test should be performed on these samples, not a rapid antigen test. In Wallonia, a large-scale pilot project was launched in which staff in all non-infected residential care centres are tested on a weekly basis using morning saliva. The project will set out to investigate whether this weekly screening can prevent outbreaks. In Antwerp, in collaboration with the University of Liège, saliva PCR tests are being compared with deep-nose PCR tests in secondary schools. If saliva is sufficiently reliable as a means of diagnosing COVID-19, this offers a more child-friendly method of collection.
Self-testing is not permitted by law for the time being, but may possibly become part of the testing strategy in due course.
Other testing methods (e.g. use of tracking dogs and breath tests) are being investigated.

Where can rapid antigen tests be used now or in the coming weeks in the context of public health?

The tests can be used immediately in hospitals on symptomatic patients under the responsibility of the clinical biology laboratory (under the pre-existing legal framework). In some hospitals, these tests are also already in use.
During the coming weeks, pilot projects will be set up to deploy rapid antigen tests for the testing of symptomatic patients in test and triage centres and general practitioners' practices. The aim of this pilot project is to investigate the framework conditions (e.g. logistics) for the introduction of rapid tests in primary medicine, and to collect information for the further roll-out of this testing strategy.
The tests can be used immediately for the diagnosis of infections in asymptomatic persons as part of a cluster investigation in group settings with a low-risk profile, such as schools, businesses, sports clubs and special youth care (i.e. not in care facilities). In secondary schools, the main aim is to help ensure the continuity of activities. Indeed, sometimes classes are already being closed when at least two children are COVID-19 positive - regardless of whether those two cases are epidemiologically linked or not. This can result in a large number of pupils/teachers being quarantined and in classes being closed when that may not be necessary. The use of rapid antigen tests provides a solution for the rapid screening of pupils and teachers/school staff in clusters and will keep classes open. Pupils and teachers/staff with a positive test result will then be quarantined more quickly, limiting the risk of a further spread of the virus.
In Flanders, the use of rapid tests will get under way immediately in care facilities (such as residential care centres) in the case of symptomatic residents, but will always be used in combination with PCR until there is sufficient knowledge about the reliability of these rapid antigen tests. In addition, a pilot project will be set up in the coming weeks to evaluate the use of antigen tests in the context of cluster investigation, also in combination with PCR. This ought to allow outbreaks to be detected and contained more quickly.
Finally, a pilot project will be launched in Flanders in the coming weeks into the use of rapid tests for the testing of high-risk contacts in schools at the start of their quarantine, after they have been identified as part of the contact tracing carried out by the pupil guidance centre (CLB). Testing high-risk contacts more rapidly will enable secondary infections to be detected more quickly. However, a negative result on the rapid test cannot be a reason for stopping quarantine.

In what areas is insufficient scientific evidence currently available that rapid antigen tests are useful?

Preventative screenings. There are two scenarios for repeated testing using rapid tests: universal testing or
the targeted testing of at-risk groups (increased risk of clusters and/or vulnerable persons). As part of a European collaboration, led by Prof Goossens, models will be developed in the coming weeks to investigate the feasibility of these scenarios.
Diagnostics based on the exclusive use of antigen rapid tests in high-risk settings such as care institutions, except for the validated pilot projects. The PCR test will remain the designated form of testing to be used in this setting until further notice.
Testing of asymptomatic high-risk contacts during quarantine, returning travellers, etc.

What about the use of rapid antigen tests in other situations?

Testing outside the public health framework (i.e. outside the test indications as published by Sciensano) cannot be prohibited. Initiatives have already been launched to use rapid tests for the organisation of events, such as sports competitions. We wish to emphasise that based on current scientific knowledge, rapid antigen tests cannot be used as conclusive evidence of the absence of a COVID-19 infection in a random population. At most, one can say that on the day of a negative test, the person concerned was possibly not contagious. This means that a negative test in an asymptomatic person:

is not conclusive proof that the person concerned is not infected with COVID-19.
cannot at any time be a reason not to respect the basic rules, to refuse quarantine or to stop it prematurely.

This is one of the reasons why rapid antigen tests outside the Sciensano guidelines will not, under any circumstances, be reimbursed by health insurance (examples of these include tests carried out in the context of travel, the organisation of events or in an economic context).

Regardless of the situations in which the rapid antigen tests are used, the accurate recording of the test results is a minimum and necessary condition. It is important that the results of the rapid tests are stored centrally. That way, they can be passed on to contact tracing, because the high-risk contacts of the infected persons detected by a rapid test will also need to be contacted for testing and the necessary quarantine. In addition, it is important that when a rapid test is carried out by a school doctor or company doctor, for example, the general practitioner or the patient themselves can find out the results. To that end, a separate results database is being set up, as well as an IT system that achieves this goal without imposing too great an additional administrative burden on the doctors and the sample collection centres. This additional system should be operational by the beginning of December.

Finally, a statutory framework is being developed that will lay down the conditions for the provision and take-up of testing, the implementation of tests and for the analysis that is carried out. A statutory framework is necessary because rapid tests that are less reliable are coming onto the market. That framework will also regulate the recording of the results at Sciensano and the reimbursement of the cost of the tests.