This is an open-label, randomized, parallel-controlled clinical trial conducted in people aged 18 years and older to evaluate the immunogenicity and safety of two SARS-CoV-2 bivalent vaccines constructed by adenovirus type 5-based or mRNA-based technics.

The clinical trial plans to recruit 450 subjects aged 18 years and above with an interval of ≥ 3 months between the previous dose of SARS-CoV-2 vaccine immunization and receive one dose of inhaled prototype strain and omicron BA.4/5 bivalent recombinant SARS-CoV-2 vaccine (adenovirus vector type 5) (Ad5-NCO5T-IH), beta strain and omicron BA.4/5 bivalent SARS-CoV-2 mRNA vaccine (mbO5) or inhaled prototype recombinant SARS-CoV-2 vaccine (adenovirus vector type 5) (Ad5-nCoV-IH) for follow-up until 6 months after vaccination.

Inclusion Criteria:

1. Volunteers aged 18 and above at the time of screening;
2. Volunteers can provide with informed consent and sign informed consent form (ICF);
3. Have received COVID-19 vaccine, and the interval between the last vaccination ≥ 3 months.

Exclusion Criteria:

1. Those with convulsions, epilepsy, encephalopathy and serious neurological diseases (such as transverse myelitis, Guillain-Barre syndrome, demyelinating disease, etc.) in the past five years;
2. Those who are allergic to the active ingredient, any inactive ingredient, or substances used in the production process of the research vaccine, or those who are allergic to the similar vaccines previously; Those who have had severe allergic reactions to vaccines in the past (such as acute allergic reactions, angioedema, dyspnea, etc.), and have any previous history of severe allergies to vaccines, foods, drugs, such as: urticaria, anaphylactic shock, skin eczema, allergic dyspnea, angioedema, etc. or a history of asthma;
3. Those who have previously suffered from severe heart diseases such as myocarditis and pericarditis;
4. Those who have experienced vaccination-related hospitalization or emergency care after previous vaccination;
5. Female urine pregnancy test positive or lactating volunteers, volunteers or their partners have not taken effective contraception 2 weeks before screening or have a pregnancy plan within 6 months;
6. Fever, axillary body temperature≥ 37.3°C;
7. Those with suspected symptoms of COVID-19 in the past 3 months (fever, cough, muscle pain, loss of smell or taste, etc.);
8. Investigators judge that they have known or suspected concomitant serious diseases with unstable drug control, including: respiratory diseases, tuberculosis, acute infection or active chronic disease, liver and kidney disease, cardiovascular disease (cardiopulmonary failure), hypertension (systolic blood pressure ≥ 160 mmHg, diastolic blood pressure ≥100 mmHg), malignant tumors, infectious or allergic skin diseases;
9. No spleen or functional spleen;
10. Thrombocytopenia, bleeding disorders, or other coagulation disorders (which may cause contraindications to intramuscular injection);
11. Immunosuppressant therapy, anti-allergic therapy, cytotoxic therapy, inhaled corticosteroids (excluding corticosteroid spray therapy for allergic rhinitis, superficial corticosteroid therapy for acute non-complicated dermatitis) in the past 6 months;
12. Suffering from nasal or oral diseases, such as acute rhinitis (sinusitis), allergic rhinitis, mouth ulcers, throat redness and swelling, etc.;
13. Have received blood products within 3 months prior to receiving the test vaccine;
14. Have received other vaccines or investigational drugs within 1 month prior to receiving the test vaccine;
15. Are receiving anti-tuberculosis treatment;
16. Those with a history of COVID-19 infection in the past 3 months;
17. Those who have a positive test result of the novel coronavirus antigen at the time of screening;
18. Those with positive HIV infection results at screening;
19. Participated in other interventional studies of lipid-containing nanoparticles;
20. According to the judgment of the investigator, due to various medical, psychological, social or other conditions, it is contrary to the trial protocol, or affects the volunteers' signing of informed consent.