Study design and participants
ADVERSE EVENT, DISEASE
This phase 4, open-label, observational study was conducted in Shaanxi Province, China, from October 2020 to March 2021. Safety observations after vaccination were carried out by a combination of active surveillance and passive surveillance. Active surveillance collected safety data by selecting some vaccination units in four cities of Shaanxi Province (Baoji City, Xianyang City, Yan’an City, and Hanzhong City) as the research sites, while passive surveillance collected Adverse Events Following Immunization (AEFI) data after vaccination from the "Chinese National AEFI Information System (CNAEFIS)".Eligible participants were freshmen of junior high school who were not above 14 years old and were able to complete safety follow-ups and to adhere to research procedures. Written informed consent was obtained from the subject’s parents or guardians before enrollment. This study was approved by the ethical review committee of the Shaanxi Provincial Center for Disease Control and Prevention (2020-001-08). The trial was registered with ClinicalTrials.gov (NCT05145166).