EVEN people with mild coronavirus illness develop antibodies, researchers say.
Scientists in France discovered most people have traces in their blood – suggesting they may have some level of immunity to Covid-19.
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This gives hope that antibody tests – a simple finger-prick blood test – will be effective in showing whether someone has had the bug and has developed some potential protection against reinfection.
Researchers from the Pasteur Institute, in Paris, made the discovery after analysing the blood of more than 160 medics at two hospitals in Strasbourg, eastern France, who contracted coronavirus in early March.
The participants, comprised of doctors, nurses, dentists and other medics, were on average 32 years old, and had mild Covid-19 illness.
Anyone who was severely ill with the disease was removed from the study, as the researchers wanted to focus on patients with mild disease.
This is because there is little known about their immunity even though they make up to 80 per cent of cases, according to the World Health Organisation.
The researchers used two separate antibody tests to look for antibodies, which the body makes as a way to fight the infection.
The first test was a commercially available one, which generally are less accurate, while the second test was developed by the institute to identify antibodies, and the ability of those antibodies to kill the virus.
The first test, a rapid immunodiagnostic test, found antibodies in 153 (95.6 per cent) of the samples.
The more robust second test detected antibodies in 159 (99.4 per cent) volunteers.
However, it failed to detect antibodies in a 58-year-old man.
When looking at the antibodies' ability to neutralise the virus, they appeared to grow stronger in the weeks after infection.
Neutralising antibodies – which bind to the virus and inactivate it, rather than 'tag' it for other immune cells – were detected in 79 per cent of samples 13-20 days after symptoms started.
This rose to 98 per cent after 28-41 days.
What is an antibody test?
When a person gets coronavirus, the body starts making specially designed proteins called antibodies in response – as a way to fight the infection.
After they recover, those antibodies float in the blood for months, maybe even years.
That's the body's way of defending itself in case it becomes infected with the virus again.
So an antibody test specifically looks for antibodies which will be able to tell whether you've already been exposed to Covid-19.
Anyone who has already had the illness is presumed to be immune to getting it again – at least, in the intermediate term.
This would allow them to go back to work safe in the knowledge that they are unlikely to become infected again or pass the virus on.
The check that has been developed for Covid-19 is a finger-prick blood test, with the samples sent to laboratories and results available within a few days.
Dr Hilary Jones, a GP and resident doctor on Good Morning Britain, explained that it works "almost like a pregnancy test, except you need a drop of blood".
These tests are being developed by several different firms and Public Health England (PHE) is also working on its own test.
Olivier Schwartz, one of the leading researchers, told the French newspaper Le Monde: "It is a fair assumption that the majority of individuals with mild Covid-19 generate neutralising antibodies within a month after onset of symptoms.
"The neutralising activity is present much later than the appearance of antibodies and this is encouraging.
"Although not yet demonstrated, several lines of evidence suggest that the presence of neutralising antibodies may be associated with protective immunity for Sars-CoV-2 infection."
The findings, which have yet to be peer-reviewed, have been published on MedRxiv.
The study did not look at blood samples any later than 40 days after symptoms, so it was not established how long antibodies last for.
The majority of individuals with mild Covid-19 generate neutralising antibodies
Several countries, including the UK, have pinned their hopes on tests that identify coronavirus antibodies to decide who is immune and can go back to work.
However, antibody testing has been plagued with setbacks since the start of the outbreak – due to the difficulty of finding a test with enough reliability.
Earlier this week, Superdrug pulled its home coronavirus antibody test kits over fears that it could give false results.
Labs were told to stop processing the tests, as well as other commercial antibody kits, that tell whether you've already been exposed to Covid-19 through a finger-prick blood sampling.
The Medicines and Healthcare products Regulatory Agency (MHRA), which governs the rules over medicines used in the UK, has said Brits should ignore any result they get from the private kits.
The Government’s testing chief warned Brits not to buy antibody test kits at the weekend, saying people should wait for official checks to become available.
Professor John Newton warned: “The public need to be aware that those tests are not the same as those we have evaluated and approved for use.
“The laboratory-based tests have a much higher standard of accuracy.
"We wouldn't recommend at the moment that people rely on the tests that are becoming widely available.
“My advice would be to wait until we have better tests which will be available in a similar form very soon, though they are still under evaluation at the moment.”
The Government announced last week that more than ten million antibody kits have been bought in a deal with pharmaceutical firm Roche.
They will first be rolled out in hospitals and care homes.
These were planned to be rolled out to the public soon after – but there are concerns this will not go ahead.
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