UK researchers have developed a single blood test that not only detects antibodies but also measures other signs of an immune system response to the virus, Reuters news agency reported on Tuesday.

This is reportedly useful as not everyone produces measurable amounts of COVID-19 antibodies after infection or vaccination.

Specifically, the blood test measures T cells, powerful immune cells that learn to recognise the virus either after encountering it during infection or through vaccination.

As a part of the new test, blood samples are exposed to replicas of small pieces of the virus. If the T cells in the blood sample recognise these pieces, they are triggered to produce molecules that can be easily measured, such as the inflammatory protein interferon-gamma.

Martin Scurr of Cardiff University School of Medicine, co-author of a report published in Immunology, stated: "The test is very sensitive and seems to be accurate," adding that the test is easy to employ and should play a very useful role in monitoring antibody and T cell responses to the virus.

"However, it remains to be determined what level of antibody and T cell response against the virus might protect from future infection and COVID-19," Scurr also stated.