Berlin (AFP)

Dawn is pointing its nose in Berlin and Lothar Kopp, 65, is already lining up in front of a clinic in the Reinickendorf district of the German capital.

With a handful of others, he waits - within two meters of safety distances and with a mask on his face - to undergo a coronavirus test like no other: without being sick, he wants to know he previously caught the virus and therefore developed immunity.

"If I have ever had coronavirus, I cannot infect other people," he said, hoping that a positive antibody test would allow him to visit his old mother safely. of contagion.

As deconfinement begins in several countries, experts have raised the possibility of "immune passports" allowing those who have developed protection against the virus to return to work before others.

Large studies are underway in Germany, where tens of thousands of these tests have been performed. Elsewhere, the level of immunity of the population also interests researchers and political decision-makers.

To find out how many people have already been infected, New York State will launch tests "aggressively", announced Governor Andrew Cuomo last week.

The American regulator has even authorized manufacturers to sell their tests without formal authorization.

- Caution -

The World Health Organization and other doctors have, however, warned of doubts about the accuracy and reliability of these tests, an unknown concerning the new coronavirus being notably the duration of a possible immunity.

A positive serological test would therefore not mean the end of the danger.

"Once we have valid tests, we still will not know whether a positive result really means protection against the disease, or how long this protection will last," said a spokeswoman for WHO AFP.

For Matthias Orth, member of the executive board of the German Federation of Biological Physicians (BDL), another big problem is the quality of the results: "false negatives" are possible, for example.

"There are also fairly common coronaviruses that do not cause serious illness" and that can bias the result, "he explains.

In any case, rapid serology tests promising a result in 15 minutes with a few drops of blood taken at home on the finger are "nonsense," says Mr. Orth.

Better tests will be developed in the coming weeks but "we are not there yet", he insisted.

- 70,000 tests -

On the other hand, while large studies like those in Germany can determine the proportion of the population that has been infected, the limitations of the tests currently available make it impossible to determine with certainty the proportion of people who are truly immunized.

However, studies, like the one launched last weekend in Munich on 3,000 households chosen at random, are being watched with great interest.

Separately, in Gangelt, in the Heinsberg region where the first large outbreak of Covid-19 had developed in Germany, researchers determined that 14% of the inhabitants had been infected.

In addition to studies, German pharmaceutical groups have also launched their serological test offers.

Some 70,000 of these tests have already been carried out in 54 German laboratories, according to the federation of ALM aggregated laboratories.

For doctor Ulrike Leimer-Lipke, who has been offering immune status tests since mid-March in Reinickendorf, these tests "make sense, because that's how we will know who is immune."

According to her, "it's very important to know this for those who have parents or grandparents they love."

© 2020 AFP