Negative antibodies may not mean immunity to the virus

PATIENTS who test negative for antibodies may still have immunity against coronavirus, scientists have said.

White blood cells in the mouth and throat known as T cells, which fight off viruses, are produced when a person comes into contact with Covid-19, acting as a first line of defence, according to a study in the academic journal Cell.

This means the body may never need to produce antibodies to fight off the virus, and blood will test negative.

However, the person has still successfully fought off the virus and is likely to have a layer of protection against future infection, it is argued.

A “dream test” would be an oral swab that can detect whether T cells have been activated, giving a clearer indication of who has been exposed to coronavirus, scientists explain.

The probe would be placed under the tongue for 60 seconds and it would give two readings, indicating whether the person currently has the virus or not, and whether they have a good or poor immune response to it. Prof Karol Sikora, an oncologist of 50 years and chief medical officer at Rutherford Health, told The Sunday Telegraph that he and his wife both tested negative for coronavirus antibodies, despite being convinced they had both come into contact with the virus.

“I was sure I would test positive, and my wife went through the deep depression when she tested negative,” he said.

“But there may be other mechanisms involved – T cells in the saliva and back of the throat that actually kill the virus before it gets in. Without the antibodies showing up on the test, the person would still have some layer of protection. I think I’m protected.”

Superdrug was the first high street retailer to offer a finger prick antibody testing kit, costing £69, which can be carried out at home. But sales were halted following a warning from the Medicines and Healthcare products Regulatory Agency that they are not reliable enough.

Meanwhile, private clinics have been offering coronavirus antibody tests for around £100, but the sensitivity of the tests has also been called into question.

Dr Bharat Pankhania, a senior clinical lecturer at the University of Exeter Medical School, said antibody tests can be unreliable and “immunity certificates are a no-no”.