Covid-19: how antigen tests should revolutionize screening

Endless queues to carry out Covid tests will soon be history, even if the deadlines are getting shorter in the big cities. The High Authority for Health (HAS) today issued its opinion on the use of antigenic tests, during an online press conference. She advocates the massive use of this form of testing to more effectively detect Covid-19 in people who show symptoms.

#Communicated | #COVID19 After a favorable opinion on the use of antigen tests on nasopharyngeal samples in symptomatic patients ➡ HAS positions them in the virus detection strategy

⚠ Objective: test more people, faster

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– High Authority for Health (@HAS_sante) October 9, 2020

Speed, the main advantage of antigen testing

Until now, the most used solution in France was to use RT-PCR tests. However, with the mass screening strategy desired by the government, the wait has become longer and longer. While in practice the results had to be sent to patients within three days, in reality the wait could reach up to eight days. This delay, which is explained by the overload of the analysis laboratories, makes the results obsolete because they exceed the 72 hours of validity of the test. Worse still, if the test is positive, the person concerned will have had time to contaminate others, thus creating contact cases who will also have to carry out Covid tests, which themselves will take time to arrive. It is to get out of this infernal spiral, and unclog the analysis laboratories, that the HAS recommends using antigenic tests.

The antigen test determines whether or not we are carriers of the coronavirus thanks to our antigens, focusing on the antibodies that our body produces. As with the PCR test, the antigen test is done using a nasopharyngeal sample, however, the results are available after half an hour, compared to 72 hours on average for the PCR test. Antigen test results are considered reliable for up to 4 days after a potential infection. Thanks to their ease of use, they can be easily used by all types of health professionals (nurses, doctors, pharmacists, analysis laboratories, etc.).

Nevertheless, antigenic tests will only be used as a priority in three cases:

– For those at risk of developing a severe form of the disease, such as people over the age of 65 or those with long-term conditions. Even if the antigen test is negative, the High Authority advises them to do a PCR test to confirm the results, so as not to miss any potential false negatives.

– For patients who have symptoms and who cannot benefit from a PCR test within the first 48 hours, HAS invites them to take an antigen test. If the result is positive, it is not necessary to do a PCR test to reconfirm the diagnosis.

– For patients without symptoms who are not contact cases but who regularly move within closed and confined spaces (universities, nursing homes or companies for example). In this case, it is the aspect of speed of access to results that is taken into account. The interest here is to flush out an epidemic focus (cluster) as quickly as possible by testing a large number of people.

In addition to its speed, the other advantage of the antigen test compared to the PCR test lies in its ability to test large populations at one time. Since they require almost no equipment, antigen tests can be deployed quickly. Thus, it becomes easier to identify and treat patients quickly, which has the effect of quickly “breaking up” any epidemic outbreaks.

The PCR test remains relevant

If the antigen test has undeniable advantages of speed and reliability compared to the PCR test, the latter will not be abandoned. It will always be used in addition to the antigen test to confirm cases of coronavirus, in particular for people who would be false positives or false negatives. In addition, if a patient has had symptoms of the coronavirus for more than four days, he will be redirected to the PCR test, because the HAS considers that the results of the antigen test are no longer sufficiently reliable after this period.

Finally, two unknowns remain to be clarified. The first lies in the financing of this measure, which has not yet been decided between the National Health Insurance Fund and the Ministry of Health. The second, and surely the most important, is the availability of these tests on a large scale. The High Authority for Health did not wish to give a precise date for the generalization of the device, simply speaking of a clarification from the ministry which should arrive in the coming days.