I have posted many times about T-cell immunity against Covid-19. This new study (SARS-CoV-2 infection induces long-lived bone marrow plasma cells in humans), just published two days ago, confirms that “circulating resting memory B cells directed against the S protein were detected in the convalescent individuals” 11 months after first symptoms.
You can read more about it in this blog published on the Washington University School of Medicine website.