HOUSEMATES COULD DEVELOP SILENT IMMUNITY

UP to three-quarters of people in a household unit 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.

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 rapidly.

It is currently estimated that up to 10% of people 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 study from Strasbourg University Hospital in France looked at seven families.

It found 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.

Up to 10% of people may be immune