A study has shown that up to three quarters of people in a household may silently develop immunity to coronavirus while living with a COVID-19 patient.
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.
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.
Scientists found that six out of eight have tested negative of those living with someone detected with coronavirus when they were tested for antibodies in their blood.
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, Dailymail UK reported.
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, said immunology experts.
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.
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 researchers of Strasbourg University Hospital in France looked at seven families in their latest study after finding the family members’ 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.
