Immunogenicity and Safety of a SARS CoV 2 Inactivated Vaccine in Healthy Adults Aged 18 59 years: Report of the Randomized, Double blind, and Placebo controlled Phase 2 Clinical Trial

BACKGROUND The top priority for the control of COVID-19 pandemic currently is the development of a vaccine. A phase 2 trial conducted to further evaluate the immunogenicity and safety of a SARS-CoV-2 inactivated vaccine (CoronaVac). METHODS We conducted a randomized, double-blind, placebo-controlled trial to evaluate the optimal dose, immunogenicity and safety of the CoronaVac. A total of 600 healthy adults aged 18-59 years were randomly assigned to receive 2 injections of the trial vaccine at a dose of 3 μg/0.5 mL or 6 μg /0.5mL, or placebo on Day 0,14 schedule or Day 0,28 schedule. For safety evaluation, solicited and unsolicited adverse events were collected after each vaccination within 7 days and 28 days, respectively. Blood samples were taken for antibody assay. RESULTS CoronaVac was well tolerated, and no dose-related safety concerns were observed. Most of the adverse reactions fell in the solicited category and were mild in severity. Pain at injection site was the most frequently reported symptoms. No Grade 3 adverse reaction or vaccine related SAEs were reported. CoronaVac showed good immunogenicity with the lower 3 μg dose eliciting 92.4% seroconversion under Day 0,14 schedule and 97.4% under Day 0,28 schedule. 28 days after two-dose vaccination, the Nab levels of individual schedules range from 23.8 to 65.4 among different dosage and vaccination schedules. CONCLUSIONS Favorable safety and immunogenicity of CoronaVac was demonstrated on both schedules and both dosages, which support the conduction of phase 3 trial with optimum schedule/dosage per different scenarios. ### Competing Interest Statement Mixed competing interests: All authors have completed the ICMJE uniform disclosure form at [www.icmje.org/coi_disclosure.pdf][1] and declare: Weidong Yin is CEO of Sinovac Biotech Co., LTD, and Gang Zeng, Yaling Hu, Qianqian Xin, Weixiao Han, Xuejie Gong, Yuansheng Hu and Hengming Zhang are employees of Sinovac Biotech Co., LTD, which provides financial support for the current study; Guoliang Cui, Xiaojuan Lian and Qiang Gao are employees of Sinovac Life Sciences Co., Ltd., which provides financial support for the current study.; no other relationships or activities that could appear to have influenced the submitted work. ### Clinical Trial NCT04352608 ### Clinical Protocols ### Funding Statement National Key Research and Development Program (2020YFC0849600) Beijing Science and Technology Program (Z201100005420023) ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: The ethics committee of the Jiangsu Provincial Center for Disease Control and Prevention All necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as [ClinicalTrials.gov][2]. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines and uploaded the relevant EQUATOR Network research reporting checklist(s) and other pertinent material as supplementary files, if applicable. Yes All the data in this manuscript is available. [1]: http://www.icmje.org/coi_disclosure.pdf [2]: http://ClinicalTrials.gov