Participants and vaccination protocol
The participants from a randomized, case-driven phase 3 clinical trial (registered clinical trials No. NCT04582344), which was initiated on Sept 15, 2020, and terminated on Jan 13, 2021, were enrolled. A group of volunteers who participated in the phase 3 clinical trial was followed up for T cell responses for an additional four months after signing the informed consent. Peripheral blood samples were collected from the placebo group and from the individuals who were vaccinated with the inactivated SARS-CoV-2 vaccine (CoronaVac, Sinovac Life Sciences Beijing, China) on the days 7 and 120 following the second dose. CoronaVac consists of β-propiolactone-inactivated whole-virion of SARS-CoV-2 CZ02 strain (3 μg/0.5 mL/dose), which is produced in African green monkey kidney (Vero) cells, and aluminum hydroxide (0.45 mg/mL) as adjuvantData of the volunteers enrolled in the study.