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During the press conference of the Interfederal Coronavirus Crisis Center on November 30, particular attention was paid to the various existing covid tests, while the test strategy will allow a new type of test, the test. antigenic.
The antigen test: fast, but not very sensitive
A rapid test is a test performed outside the laboratory, the results of which are available within 15-30 minutes, following an analysis carried out on site (at the collection center, or at the primary care physician). There are two types of quick tests:
- The serological test, which will detect antibodies or immune cells that will fight the virus.
- The antigen test, which will detect antigens, or molecular fragments of the virus, which have the distinction of being very specific to the virus. It is this antigen that the immune cells will recognize to identify and specifically attack it. (The PCR test identifies pieces of the virus genome or its RNA).
But these tests cannot be used always or in all cases.
►►► Covid-19 screening: what are the different types of tests and what are their advantages and disadvantages? (infographic)
Typically, the serological test will simply show that the body has developed an immune response to covid-19: as this immunity can last for several months (between three and six months according to the latest research), this test does not tell if you are contagious or if you are a carrier of the virus. The serological test is also ineffective at the beginning of the disease, when the body has not yet produced antibodies. It is therefore not a test to evaluate if you are sick or the progress of an epidemic, it only serves to evaluate the immunity developed.
The antigen test will demonstrate the presence of the virus or virus fragments. But they are much less sensitive than PCR tests, which means they need a greater amount of virus to be able to detect it. The risk of false negatives is therefore greater than with PCR tests, but it remains interesting because a positive result means that you are contagious.
The timing of the antigen test is very important: only symptomatic people, within the first five days of the onset of symptoms, can be tested with the antigen test, because the amount of virus is therefore considered high enough to be detected .
“These tests could potentially be of interest in group surveillance, particularly of people in contact with risk groups, if tested frequently. These are ongoing studies in several communities.” explique Yves Van Laethem.
Self test: very unreliable
As the name suggests, self-tests are performed by the patient himself and the results are available in minutes, without the intervention of a healthcare professional.
“These self-tests are less reliable, less sensitive, less accurate than laboratory tests, warns Yves Van Laethem. These self-tests can therefore give a false sense of security, and participate in the spread of the virus, or conversely, in the case of a false positive, give a false sense of concern “.
“There is currently only one compliant self-test in Europe, but because it detects antibodies it is not used to control the spread of the virus.”
The spokesperson specified that to be legal in Europe, a self-test (covid or not) must bear a European marking, consisting of the letters “CE” followed by four numbers. If the marking has no numbers it means that the test is not intended for the general public but rather for medical personnel, who are able to correctly interpret the results.
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