“Test, test, test! The message from the World Health Organization (WHO), regularly delivered since mid-March, seems to have finally been heard in France. Rapid screening kits to detect Covid-19 disease are increasing, the government having ordered five million.
The Minister of Health, Olivier Véran, also announced that serology tests would soon be available. Serology is essential to measure the extent to which the population has been infected with the new coronavirus. It will also make it possible to say if all the inhabitants are sufficiently immunized to start a progressive deconfinement of the country, under bell until April 15 minimum.
I ordered 2 million tests which will be delivered to us in April. They are an essential link in our strategy to massively test the French and to make screening available to the most vulnerable in our nursing homes. pic.twitter.com/QmNMkclXxB
– Olivier Véran (@olivierveran) March 26, 2020
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Unlike the test by nasal swab called PCR or rapid test, serology consists in taking a blood sample (usually by a blood test) to look for the presence or not of antibodies. These are produced when the human body is infected with a virus. They appear in the blood and are detectable “from the fifth day after infection, so very early,” explains Parisian Antoine Flahault, professor of public health at the University of Geneva. A positive result proves that the person has been infected.What are serology tests?
Unlike the nasal test, which can be false negative (in an infected person), serology has a much smaller margin of error.
Why are they important for measuring the epidemic?
This technique has the advantage of also counting all people with Covid-19 but who have not had symptoms. In addition to not having had a nasal test and not being counted in the statistics, these individuals did not even suspect that they were infected. And there are many: it is estimated that these asymptomatic patients represent between 30 and 60% of all infected people.
Serology will also make it possible to obtain large-scale epidemiological data (description of the affected population, case fatality rate, etc.).
Why can they help alleviate containment?
Olivier Véran assured him, Thursday March 25 on France 2: serology will “prepare the country for the essential phase of deconfinement, where we should be able to tell the French if they have had the disease or if they haven’t had it. ” It is “a very precious help in managing deconfinement”, adds Antoine Flahault.
“If we realize that a large part of the population is immunized, then we can get out of confinement without risk because the population will act as a natural barrier against any new major epidemic,” details the epidemiologist. This is called “collective immunity” or “gregarious immunity”.
By “large part” of the population is meant between 50 and 70%, in the case of the coronavirus. This rate depends on the contagiousness of the virus, the “R zero” in scientific terms, that is to say the number of people that an infected person can infect.
