TNFRSF9 and COVID-19: CD8+ cell responses, determined as the expression of CD69+ and CD137+, were detected in 80% of COVID-19 patients and 70% of vaccinees six weeks after the first vaccine dose (3 weeks after the second dose), in 67% of vaccinees 3 months after the first dose, and in 53% of vaccinees 6 months after the first dose (Figure 2B).