Study on Heterologous Prime-boost of Recombinant COVID-19 Vaccine (Ad5 Vector) and RBD-based Protein Subunit Vaccine

• recombinant Ad5 vectored COVID-19 vaccine (Biological), also known as Ad5-nCoV: This vaccine contains 5×10\^10 virus particles of recombinant replication defective human type-5 adenovirus expressing SARS-CoV-2 S protein, which is produced by CanSino Biologics Inc. It is a liquid dosage form, 0.5 ml / bottle.
• RBD-based protein subunit vaccine (ZF2001) against COVID-19 (Biological), also known as ZF2001 vaccine: This is a recombinant tandem-repeat dimeric RBD-based protein subunit vaccine (ZF2001) against COVID-19, made by using CHO cell, 25μg/dose, produced by Anhui Zhifei Longcom Biopharmaceutical Co.,Ltd.
• trivalent split influenza vaccine (Biological): This vaccine contains 15 μ g H1NI, 15 μ g H3N2 and 15 μ g B-series hemagglutinin, produced by Dalian Aleph Biomedical Co., Ltd.It is a liquid dosage form, 0.5 ml / bottle.

Primary outcomes

• Incidence of solicited adverse events within 7 days after vaccination. [Within 7 days after vaccination]: Incidence of solicited adverse events within 7 days after vaccination.
• GMT of neutralizing antibodies against live SARS-CoV-2 virus at Day 14 after the booster vaccination. [At Day 14 after the booster vaccination]: GMT of neutralizing antibodies against live SARS-CoV-2 virus at Day 14 after the booster vaccination.

Secondary outcomes

• Incidence of adverse reactions within 28 days after vaccination. [Within 28 days after vaccination]: Incidence of adverse reactions within 28 days after vaccination.
• Incidence of adverse events within 28 days after vaccination. [Within 28 days after vaccination.]: Incidence of adverse events within 28 days after vaccination.
• Incidence of unsolicited AE within 28 days after vaccination. [Within 28 days after vaccination.]: Incidence of unsolicited adverse events within 28 days after vaccination.
• Incidence of serious adverse events(SAE) from the first dose to the 6 months after completing the last dose of vaccination. [From the first dose to the 6 months after completing the last dose of vaccination.]: Incidence of serious adverse events(SAE) from the first dose to the 6 months after completing the last dose of vaccination.
• GMT of binding antibodies against SARS-CoV-2 S and RBD protein measured by ELISA at day 14, day 28 after the second vaccination, and day 14, month 6 after the third vaccination. [at day 14, day 28 after the second vaccination, and day 14, month 6 after the third vaccination.]: GMT of binding antibodies against SARS-CoV-2 S and RBD protein measured by ELISA at day 14, day 28 after the second vaccination, and day 14, month 6 after the third vaccination.
• Proportion of the participants with at least a four-fold increase of the binding antibodies against SARS-CoV-2 S and RBD protein at day 14, day 28 after the second vaccination, and day 14, month 6 after the third vaccination. [at day 14, day 28 after the second vaccination, and day 14, month 6 after the third vaccination.]: Proportion of the participants with at least a four-fold increase of the binding antibodies against SARS-CoV-2 S and RBD protein at day 14, day 28 after the second vaccination, and day 14, month 6 after the third vaccination.
• Fold increase of binding antibodies against SARS-CoV-2 S and RBD protein at day 14, day 28 after the second vaccination, and day 14, month 6 after the third vaccination. [at day 14, day 28 after the second vaccination, and day 14, month 6 after the third vaccination.]: Fold increase of binding antibodies against SARS-CoV-2 S and RBD protein measured by ELISA, as compared to baseline, at day 14, day 28 after the second vaccination, and day 14, month 6 after the third vaccination.
• GMT of neutralizing antibodies against live SARS-CoV-2 virus at day 28 after the second vaccination, and day 14, month 6 after the third vaccination [at day 28 after the second vaccination, and day 14, month 6 after the third vaccination]: GMT of neutralizing antibodies against live SARS-CoV-2 virus at day 28 after the second vaccination, and day 14, month 6 after the third vaccination
• Proportion of the participants with at least a four-fold increase of neutralizing antibodies against live SARS-CoV-2 virus at day 14, day 28 after the second vaccination, and day 14, month 6 after the third vaccination. [at day 14, day 28 after the second vaccination, and day 14, month 6 after the third vaccination.]: Proportion of the participants with at least a four-fold increase of neutralizing antibodies against live SARS-CoV-2 virus, as compared to baseline, at day 28 after the second vaccination, and day 14, month 6 after the third vaccination.
• Fold increase of neutralizing antibodies against live SARS-CoV-2 virus at day 14, day 28 after the second vaccination and day 14, month 6 after the third vaccination. [at day 14, day 28 after the second vaccination and day 14, month 6 after the third vaccination.]: Fold increase of neutralizing antibodies against live SARS-CoV-2 virus, as compared to baseline, at day 14, day 28 after the second vaccination and day 14, month 6 after the third vaccination.

Other outcomes

• Types of binding antibodies IgG against SARS-CoV-2 S protein at day 14, day 28 after the second vaccination and day 14, month 6 after the third vaccination. [at day 14, day 28 after the second vaccination and day 14, month 6 after the third vaccination.]: Types of binding antibodies IgG against SARS-CoV-2 S protein at day 14, day 28 after the second vaccination and day 14, month 6 after the third vaccination.
• Cross neutralizing of the antibodies to variants of SARS-CoV-2 measured by pseudovirus neutralization test at Day 28 after the booster vaccination. [At Day 28 after the booster vaccination.]: Cross neutralizing of the antibodies to variants of SARS-CoV-2 measured by pseudovirus neutralization test at Day 28 after the booster vaccination.
• The immune cells' subgroups and germlines at Day 28 after vaccination. [At Day 28 after vaccination.]: The immune cells', such as B cells and T cells, subgroups and germlines at Day 28 after vaccination.

Sex: All, ages: 18 Years to any

Inclusion Criteria:

* The subjects ≥ 18 years old who has completed one dose of recombinant Ad5 vectored COVID-19 vaccine.
* The subjects can provide with informed consent and sign informed consent form (ICF).
* The subjects are able to and willing to comply with the requirements of the clinical trial program and can complete the 6-month follow-up of the study.
* Axillary temperature ≤ 37.0 ℃
* Individuals who are in good health condition at the time of entry into the trial as determined by medical history, physical examination and clinical judgment of the investigator and meet the requirements of these products immunization.

Exclusion Criteria:

* have a medical history or family history of convulsion, epilepsy, encephalopathy and psychosis.
* be allergic to any component of the research vaccines, or used to have a history of hypersensitivity or serious reactions to vaccination.
* Women with positive urine pregnancy test, pregnant or breast-feeding, or have a pregnancy plan within six months.
* have acute febrile diseases and infectious diseases.
* have severe chronic diseases or condition in progress cannot be smoothly controlled, such as asthma, diabetes, thyroid disease
* Congenital or acquired angioedema / neuroedema.
* have the history of urticaria 1 year before receiving the trial vaccine.
* have asplenia or functional asplenia.
* have thrombocytopenia or other coagulation disorders (which may cause contraindications for intramuscular injection).
* have the history of immunosuppressive therapy, anti allergy therapy, cytotoxic therapy or inhaled corticosteroids (excluding corticosteroid spray therapy for allergic rhinitis, and acute corticosteroid therapy without dermatitis) over the past 6 months.
* have received blood products within 4 months before injection of trial vaccines.
* have received another investigational product within one month before injection of trial vaccine.
* have received attenuated vaccine within 1 month before injection of trial vaccine except the recombinant Ad5 vectored COVID-19 vaccine.
* have received subunit or inactivated vaccine within 14 days before the vaccination with trial vaccine.
* under anti tuberculosis treatment.
* not be able to follow the protocol, or not be able to understand the informed consent according to the researcher's judgment, due to various medical, psychological, social or other conditions.

• Results publication: Jin P, Guo X, Chen W, Ma S, Pan H, Dai L, Du P, Wang L, Jin L, Chen Y, Shi F, Liu J, Xu X, Zhang Y, Gao GF, Chen C, Feng J, Li J, Zhu F. Safety and immunogenicity of heterologous boost immunization with an adenovirus type-5-vectored and protein-subunit-based COVID-19 vaccine (Convidecia/ZF2001): A randomized, observer-blinded, placebo-controlled trial. PLoS Med. 2022 May 26;19(5):e1003953. doi: 10.1371/journal.pmed.1003953. eCollection 2022 May. PMID 35617368

• Jing-Xin Li, PhD, Principal investigator, Jiangsu Provincial Center for Diseases Control and Prevention