By Denise Chow

The newly developed test focuses on the part of the immune system that confers long-term protection by prompting the body to “remember” the virus.

A newly developed blood test that measures a specific immune response in the body could help doctors gauge how much protection a person has against Covid-19, according to a new study.

The test, which focuses on the part of the immune system that confers long-term protection by prompting the body to "remember" the virus, could help make sense of the complex tangle of Covid immunity that now exists from person to person.

The test can, for instance, measure immunity regardless of whether someone has developed a level of protection from one or more natural infections or from vaccinations and booster shots. Others, who may have much lower levels of protection because they are immunocompromised, could also use the test to assess their vulnerability and see how they responded to the vaccines, said Ernesto Guccione, an associate professor of oncological sciences and pharmacological sciences at the Tisch Cancer Institute at Mount Sinai.

"Ideally, it will give you a full picture of where you stand and a comprehensive picture of your immune protection," said Guccione, one of the authors of the study published Monday.

The researchers said they are focused next on clinical trials in order to gain approval from both the Food and Drug Administration and the European Medicines Agency.

The test involves taking a small blood sample at a clinic and mixing it with snippets of proteins from the virus. Researchers then look to see if the so-called T cells are activated in the sample.

T cells are the cornerstone of the immune system's long-term memory and typically lie in wait until they detect the presence of foreign invaders. Unlike antibody levels, which can wane following vaccinations or infections, T cells can recall a virus years, and sometimes decades, later.

Whether through vaccinations or infections, T cells are primed to "recall" fragments of a virus, including from variants that can dodge protective antibodies. This means that T cells won't stop an infection from happening, but they can prevent a patient from becoming severely ill from Covid.