What are T cells, and why do they matter when it comes to preventing COVID-19 reinfection?

Despite challenges with the distribution and administration of COVID-19 vaccines, the U.S. "can and should" vaccinate up to 85% of adults by the end of summer. That's the message from infectious disease expert Dr. Anthony Fauci this morning.
If we do hit that benchmark, he says, life could return to a semblance of normalcy by the fall.
But millions in the tri-state are still competing to get a vaccine, and supply is running low. Today, New York is expected to deplete it's allotment, and many people may have their vaccination appointments canceled.
In a new study, six in 10 Americans say they don't know when or where to get a COVID-19 vaccine. The Kaiser Family Foundation report was based on surveys conducted just last week, from Jan. 11 to 18.
Over the past few months, we have been hearing about antibody tests, and how they can help determine if you have had COVID-19. But antibody testing has proved to be an imperfect measure of both past infection and immunity. But there is another test, a test for T cells that could provide us with more information.
This morning, News 12's Elizabeth Hashagen was joined by Survivor Corps founder Diana Berrent and Dr. Lance Baldo to talk about the long term effects of COVID-19 and T cells. Dr. Lance Baldo is the chief medical officer of Adaptive Biotechnologies - which developed a T cell test for COVID-19.
When a person is infected, or inoculated with a vaccine, the immune system gears up to produce antibodies that specifically target the virus. We know that over time, those antibodies naturally wane. But the immune system still holds a memory of the virus, and if it ever shows up again, cells spring into action and start to gear up a new batch of antibodies.
Dr. Baldo talks about the role of T cells and why this matters when it comes to preventing reinfection:
Antibodies wane after recovering from an illness. Berrent talks about her experience with antibody testing:
Dr. Baldo discusses why the T cell test is going to be helpful as we learn more about the virus:
When looking at the T cells, are you seeing a difference in the people who are severely ill with COVID, and the people who are either asymptomatic or have mild symptoms? Dr. Baldo responds: