To answer that question, expanded testing is needed that can determine levels of T immune cells
More than two years into the COVID-19 pandemic, scientists are still scratching their head over a basic question: Is there something they could measure to tell if people are protected?
Researchers call such measures “correlates of protection”—indicators that a person is unlikely to get seriously ill if infected by a pathogen such as SARS-CoV-2, the virus that causes COVID-19.
