New test tells you how many T cells for COVID-19 you have

A blood test that measures a key indicator of COVID-19 immunity could help you determine your risk of contracting the coronavirus and whether to get a booster shot.

The challenge: Since the start of the pandemic, individuals have had to constantly weigh the risk of contracting the coronavirus against the benefits of doing, well, practically anything: eating out, grocery shopping, going to the dentist, flying on an airplane…

Getting vaccinated lowers the risk (at least temporarily), as does contracting COVID-19 and recovering. But determining just how protected you are at any given time is still largely a guessing game, as antibody tests alone can’t determine COVID-19 immunity.

Why it matters: This uncertainty can add stress to daily life, potentially leading some people to get sick because they underestimated their risk — while others overestimate their risk and miss out on important events.

It also makes it hard to know when to get a booster shot. 

“Monitoring both [antibodies and T cells] will give us a much clearer picture [of immunity].”

Ernesto Guccione

The test: Researchers at Mount Sinai and Duke-NUS Medical School have now developed a blood test that looks at T cells instead of antibodies as an indicator of COVID-19 immunity.

After a patient’s blood sample is collected, it’s mixed with an assay containing bits of coronavirus proteins. If there are any T cells specific to the virus in the sample, this will activate them. Measuring that activation can help determine a patient’s COVID-19 immunity.

“Monitoring both [antibodies and T cells] will give us a much clearer picture [of immunity] and will hopefully inform our re-vaccination strategies,” study co-author Ernesto Guccione told TIME.

An upgrade: This isn’t the first test to look at T cells for COVID-19 immunity — the FDA approved a test called T-Detect for emergency use in March 2021 — but this new test has several advantages.

Most importantly, T-Detect only gives you a yes/no answer about whether you have T cells that react to COVID-19. But the new test can tell you the level of T cell immunity — which is potentially an indicator of how protected you are.

There are practical benefits, too: while T-Detect takes 7-10 days for results, the new blood test can be done in as little as 24 hours. It’s less work to run and costs about $50 compared to T-Detect’s $150 (though the final price may be marked up by labs).

These upgrades could make it easier to understand what’s going on with COVID-19 immunity in the whole population — how many people are immune, how long does protection last, who needs a booster and when.

“With large numbers comes clarity,” Guccione said. “That’s the hope: by using this test, we can finally get those numbers that were totally unavailable with the previous technology.”

The bottom line: The new blood test is already cleared for use in Europe, but the FDA hasn’t yet authorized its use in the US. 

“To look at the degree of intensity of T cell immunity and have that correlated with protection — we’re not at that level yet.”

Jordi Ochando

When it is authorized, it’ll be able to measure your T cell response to COVID-19, which could help you assess your infection risk, but don’t expect it to tell you exactly how protected you are against the coronavirus — at least not initially.

“To look at the degree of intensity of T cell immunity and have that correlated with protection — we’re not at that level yet,” study co-author Jordi Ochando told NBC News. “But we hope to be at some point.”

So we’ll need to wait to know precisely how to interpret the results of the test. But one benefit of a cheap, fast T cell test is that scientists could finally get enough data to understand how T cells correlate with immunity from infection or serious illness.

We’d love to hear from you! If you have a comment about this article or if you have a tip for a future Freethink story, please email us at [email protected].