Blood Test Aims to Measure COVID Immunity

Damian McNamara, MA

June 15, 2022

Editor's note: Find the latest COVID-19 news and guidance in Medscape's Coronavirus Resource Center.

A small blood sample and 24 hours might be all that's needed to find out how strong your immune system is against a first or repeat coronavirus infection.

Scientists created a test that indirectly measures your T-cell response — an important, long-term component of immunity that can last long after antibody levels fall off — to a challenge by the virus in whole blood.

The test mimics what can be done in a formal laboratory now but avoids some complicated steps and specialized training for lab personnel. This test, researchers say, is faster, can scale up to test many more people, and can be adapted to detect viral mutations as they emerge in the future.

The study explaining how all this works was published online June 13 in Nature Biotechnology.

The test, called dqTACT, could help predict the likelihood of "breakthrough" infections in people who are fully vaccinated and could help determine how frequently people who are immunocompromised might need to be re-vaccinated, the authors note.

Infection with the coronavirus and other viruses can trigger a one-two punch from the immunity system — a fast antibody response followed by longer-lasting cellular immunity, including T cells, which "remember" the virus. Cellular immunity can trigger a quick response if the same virus ever shows up again.

The new test adds synthetic viral peptides — strings of amino acids that make up proteins — from the coronavirus to a blood sample. If there is no T-cell reaction within 24 hours, the test is negative. If the peptides trigger T cells, the test can measure the strength of the immune response.

The researchers validated the new test against traditional laboratory testing in 91 people, about half of whom never had COVID-19 and another half who were infected and recovered. The results matched well.

They also found the test predicted immune strength up to 8 months following a second dose of COVID-19 vaccine. Furthermore, T-cell response was greater among people who received two doses of a vaccine versus others who received only one immunization.

Studies are ongoing and designed to meet authorization requirements as part of future licensing from the FDA.


Nature Biotechnology: "Rapid, scalable assessment of SARS-CoV-2 cellular immunity by whole-blood PCR."


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