The World Health Organization issued a warning about coronavirus testing, saying there is no evidence serological tests can show whether a person has immunity or is no longer at risk of becoming reinfected, Mike Ryan, the WHO’s top emergency expert, told a briefing on Friday.

Ryan also said that even if antibodies were effective there was little sign that large numbers of people had developed them and were beginning to offer so-called herd immunity to the broader population.

A lot of preliminary information coming to us right now would suggest quite a low percentage of the population have seroconverted (to produce antibodies), he said.

The expectation that the majority in society may have developed antibodies, the general evidence is pointing against that, so it may not solve the problem of governments.

Ryan said scientists are also still determining the length of protection antibodies might give a person who has been infected with the coronavirus.

Nobody is sure whether someone with antibodies is fully protected against having the disease or being exposed again, he said.

Plus some of the tests have issues with sensitivity, he added. They may give a false negative result.

Professor of immunology in the public hospital system in Marseilles explained that being immunized means that you have developed an immune response against a virus such that you can repulse it.

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Our immune systems remember, which normally prevents you from being infected by the same virus later on.

For some viral diseases such as measles, overcoming the sickness confers immunity for life.

But for RNA-based viruses such as Sars-Cov-2 the scientific name for the bug that causes the coronavirus disease it takes about three weeks to build up a sufficient quantity of antibodies, and even then they may provide protection for only a few months, Vivier told AFP.

At least that is the theory. In reality, the new coronavirus has thrown up one surprise after another, to the point where virologists and epidemiologists are sure of very little.

Earlier this week, World Health Organization officials said not all people who recover from the coronavirus have the antibodies to fight a second infection, raising concern that patients may not develop immunity after surviving coronavirus.

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