Conflict of interest
Authors XL, TY, YS, and YG are employed by Sinovac Biotech Co., Ltd., YZ, JL, and JS are employed by Sinovac Life Sciences Co., Ltd.The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.The authors declare that this study received funding from Sinovac Life Sciences Co., Ltd. The funder had the following involvement in the study: the study design, on-site monitoring, antibody detection, interpretation of data, the writing and review of this article.