New blood test by French lab detects Covid-19 immunity

A French laboratory is developing a blood test that can determine exactly how immune a person is to the virus SARS-CoV-2 - which causes Covid-19 - and has hailed it “a precious tool to help with deconfinement”.

27 April 2020
Normal blood tests can only detect whether a person has any antibodies to the virus - but not how effective those antibodies actually are
By Connexion journalist

The vaccination biotech laboratory Pasteur-TheraVectys, which is based in central Paris and is a “spin off” of prestigious medical research centre l’Institut Pasteur, has been developing the test as part of the institute’s wider studies into Covid-19.

Most people who have been infected with the virus SARS-CoV-2 and subsequently recovered will have antibodies against the virus in their blood.

But the World Health Organisation (WHO) has previously said that it is not clear how immune people are to a second infection - even if they test positive for antibodies - or whether everyone who gets the virus once will have the same level of immunity once cured.

Normal blood tests can only detect whether a person has any antibodies to the virus once they have been infected and cured - but not how effective those antibodies actually are.

(Blood tests are separate to polymerase chain reaction (PCR) tests, which are used to see if someone has the virus at the time of testing.)

This new blood test can “check the effectiveness of the antibodies”, thus determining not only whether antibodies are present at all, but also how immune that person is to becoming infected again, said Dr Pierre Charneau, world-renowned virology expert and founder and director of the Pasteur-TheraVectys lab.

He told newspaper Libération: “The presence of antibodies does not allow us to say whether we are protected against a second infection by the coronavirus. We have developed a ‘sero-neutralisation’ test, which detects antibodies but in fact [also] measures their capacity to stop the virus from entering into a cell.

“So this test tells us how effective the antibodies are.”

Dr Charneau explained that other blood tests can give “false positives”, and make it appear that someone is protected when they may not be.

He said: “A person may have a positive [test] for antibodies but in reality may not be protected. So far, we have done thousands of [our kind of] tests, and we have never had a false positive. After such a short time, it is very difficult to guarantee 100% reliability [but] what we are sure of is that the level of error is very low.”

The lab is now hoping to produce more of the tests on a large scale, and receive authorisation to roll the test out to members of the public in France.

Dr Charneau said: “Making this test at high speed is not a major problem. We have all the materials we need to produce several hundred thousand. A single machine at the Institut Pasteur is enough to analyse 50,000 to 100,000 samples per week.

“The idea would therefore be to increase the number of test centres across the country, to achieve a very high number of analyses [results].”

However, this does not mean that the test will become available to individuals just yet.

Dr Charneau explained: “The regulation validation procedure for personalised human diagnostic tests is longer. [Health authority] la Haute Autorité de Santé has drawn up a list of specifications that we must comply with.

“For example, it requires reliability of at least 98%. We are generally at this level [already], but it has to be demonstrated over the course of several weeks [to comply], and we are not there yet.”

Once la Haute Autorité de Santé has approved the test, it is intended that members of the public will be able to go to their local health laboratory and request the blood test, and receive results within two days.

Widespread testing of the general public has been suggested by ministers and health experts as one of the key requirements that should be in place once confinement is lifted.

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