• Adults aged 18 years and older.

• Understand the content of the Informed Consent Form (ICF), and voluntarily sign the ICF (If the participant is unable to sign the ICF on his/her own due to illiteracy, an impartial witness is needed).

• Participants who are willing and able to comply with study requirements, including all scheduled visits, vaccinations, laboratory tests, and other study procedures.

• Female participants of childbearing potential or partners of male participants:

• voluntarily agree to use effective contraception with their partners prior to the first vaccination and must agree to continue such precautions during the study until 3 months after full vaccination (including the initial set of vaccination and crossover set of vaccination). \[Effective contraception includes oral contraceptives, injectable or implantable contraception, extended-release topical contraceptives, hormonal patches, intrauterine devices (IUDs), sterilization, abstinence, condoms (for male), diaphragms, cervical caps, etc.\].

• For female participants: without childbearing potential (amenorrhea for at least 1 year or documented surgical sterilization) or have used effective contraception with a negative pregnancy test before each vaccination in this study.

• On the day of 1st dose of vaccination and 24 hours prior to vaccination, axillary temperatures \<37.3°C/99.1°F.

• Healthy participants or participants with mild underlying disease \[in a stable state without exacerbation (no admission to hospital or no major adjustment to treatment regimen, etc.) for at least 3 months prior to enrollment in this study\].