2.1.1. Participants
VIRUS, RECRUITMENT
Healthy participants aged 18–55 years were recruited through convenience sampling from WeChat, a Chinese social media platform. Three hundred fifty-eight participants enrolled in this study by completing the recruitment questionnaire in June 2020. An initial understanding of virus characteristics had been gained during this period, the epidemic had been steadily controlled in China, and the prevention and control work had been transformed from an emergency state to a regular prevention state [The participants signed the online consent form prior to study onset. This study was approved by the Peking University Committee for the Protection of Human and Animal Subjects.