Is the fourth COVID-19 vaccine dose urgently needed? Revelation from a prospective cohort study. Issue 3 (September 2022) - Xu, Qiu-Yan; Li, Qiu-Ling; Jia, Zhi-Juan; Wu, Meng-Juan; Liu, Yan-Yun; Lin, Li-Rong; Liu, Li-Li; Yang, Tian-Ci