Blood test detects coronavirus exposure without antibodies

Because not everyone produces measurable amounts of COVID-19 antibodies after infection or vaccination, 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.

Specifically, it measures T cells, powerful immune cells that learn to recognize the virus either after encountering it during infection or through vaccination. As 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 recognize these pieces, they are triggered to produce molecules that can be easily measured, such as the inflammatory protein interferon-gamma. “The test is very sensitive and seems to be accurate,” said Martin Scurr of Cardiff University School of Medicine, coauthor of a report published in Immunology. This was true even in patients with cancer, many of whom do not produce antibodies in response to vaccination. “The test is easy to employ and should play a very useful role” in monitoring antibody and T cell responses to the virus, Scurr said. “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.”