Safety, Tolerability and Immunogenicity of a Recombinant Adenovirus Type 5 Vectored COVID-19 Vaccine in Healthy Adults in China: Preliminary Report of a First-In Human Single-Center, Open-Label, Dose-Escalating Clinical Trial

Background: We aimed to assess the safety, tolerability and immunogenicity of a recombinant adenovirus type 5 (Ad5) vectored COVID-19 vaccine expressing the spike glycoprotein of a SARS-Cov-2 strain. This is the first-in-human study of a candidate vaccine against COVID-19. Methods: We conducted a single-center, open-label, dose-escalating clinical trial of Ad5 vectored COVID-19 vaccine. Healthy adults aged between 18-60 years were sequentially enrolled and allocated to receive a single intramuscular injection in one of three dose groups: 5 × 10^10, 1×10^11, and 1·5×10^11 viral particles. Safety was assessed over the next 28 days. Specific antibodies were measured on enzyme-linked immunosorbent assay (ELISA), and the neutralizing antibody responses induced by vaccination were detected by using SARS-CoV-2 virus neutralization and pseudovirus neutralization tests. T-cell responses were accessed by enzyme-linked immunospot (ELISpot) and flow-cytometry assays. Results: A total of 108 participants were recruited and received low dose, middle dose, or high dose vaccine, with 36 in each dose group. 30(83·3%), 30(83·3%), and 27(75·0%) recipients in the low dose, middle dose, and high dose groups reported at least one adverse reaction within the first 7 days after the vaccination. The most common injection-site adverse reaction was pain, the most commonly reported systematic adverse reactions were fever, fatigue, headache, and muscle pain. A majority of the adverse reactions that were reported in all dose groups were mild or moderate in severity. No serious adverse event was noted within 28 days post-vaccination. Both ELISA antibodies and neutralizing antibodies increased significantly at day 14, and peaked 28 days post-vaccination. Specific T cell response peaked at day 14 post-vaccination. Conclusions: The Ad5 vectored COVID-19 vaccine is tolerable and immunogenic. Humoral responses against SARS-CoV-2 peaked at day 28 post-vaccination in health adults, and rapid specific T cell responses were noted since day 14. Trial Registration: The study is registered with ClinicalTrials.gov, number NCT04313127. Funding Statement: National Key R&D Program of China (2020YFC10841400), National Science and Technology Major Project (2016ZX10004001, 2018ZX09201005), and CanSino Biotechnology Inc. Declaration of Interests: Mr. Gou report being employees of Tianjin CanSino Biotechnology Inc, No other potential conflict of interest relevant to this article was reported. Ethics Approval Statement: The protocol and informed consent were approved by the Institutional Review Board of the Jiangsu Provincial Center of Disease Control and Prevention. Written informed consents from all participants were obtained before screening. This study was undertaken by Jiangsu Provincial Center of Disease Control and Prevention, Hubei Provincial Center for Disease Control and Prevention and Tongji Hospital, Tongji Medical College, Huazhong University of Science and Technology in accordance with the Declaration of Helsinki and Good Clinical Practice.