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Three quarters of people who live with a coronavirus sufferer may develop 'silent' immunity without needing antibodies

Up to three quarters of people in a household may develop ‘silent’ immunity to coronavirus when one is infected, a study has shown.
The number who have suffered Covid-19 may have been hugely underestimated because tests are looking for specific antibodies in blood rather than the body’s ‘memory’ T cells that fight infection, experts say.
Six out of eight of those living with someone who tested positive for Covid-19 showed negative results when tested for coronavirus antibodies in their blood, scientists found.
Up to three quarters of people in a household may develop ‘silent’ immunity to coronavirus when one is infected, a study has shown (stock image)
Up to three quarters of people in a household may develop ‘silent’ immunity to coronavirus when one is infected, a study has shown (stock image)
But when experts tested their blood samples for T cell immunity – part of the body’s deep defences to infection, from white blood cells in bone marrow – they found that they had in fact suffered Covid-19 with mild symptoms.
Some patients’ immune systems appear to be ‘split’ by their response to the virus so that those with no antibodies in their blood react at a deeper level with a T cell response, immunology experts said last night. This raises the prospect of new checks for coronavirus that work to detect T cells in a similar way to tests for tuberculosis – with the potential for one lab to process hundreds of patients and get effective results within two days.
It is currently estimated that up to 10 per cent of the population may have immunity to the virus, based on blood antibody tests, which detect antibodies generated by blood B cells.
T cells are the body’s big weapon – released from white blood cells in bone marrow to kill viruses when the immune system needs more help. 
The latest study from Strasbourg University Hospital in France looked at seven families because their corona blood tests were unusual. 
‘Our results suggest epidemiological data relying only on detection of SARS-CoV-2 antibodies may lead to a substantial underestimation of exposure to the virus,’ said researcher Professor Samira Fafi-Kremer.
The study involves a small sample and is yet to be peer reviewed but is being closely considered by immunologists. Professor Danny Altmann, of Imperial College and the British Society for Immunology, said there was growing evidence that Covid-19 immunity looked unusual, since some people were showing immunity from ‘memory’ T cells alone.
A normal response to a virus would be for antibodies in blood – from B cells – to also be present.
It means large numbers of those infected and who had mild symptoms may be reacting in a different way to the virus that leaves them ‘silently’ immune, because they cannot be diagnosed as having been exposed to Covid-19 by current tests.


The number who have suffered Covid-19 may have been hugely underestimated because tests are looking for specific antibodies in blood rather than the body’s ‘memory’ T cells that fight infection, experts say (stock image)
The number who have suffered Covid-19 may have been hugely underestimated because tests are looking for specific antibodies in blood rather than the body’s ‘memory’ T cells that fight infection, experts say (stock image)

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