inclusion criteria: 1. aged 18 years and older. 2. able and willing to comply with all study requirements. 3. willing to allow investigators to discuss the medical history with his/her general practitioner/personal doctors and access all medical records which are relevant to study procedures. 4. healthy adults, or adults with stable medical condition who have a pre-existing medical condition that does not meet any exclusion criteria. a stable medical condition is defined as disease not requiring significant change in therapy or hospitalization for worsening disease during the 3 months before enrollment. 5. for females of childbearing potential only, willing to practice continuous effective contraception until 90 days after the final dose vaccination, and have negative pregnancy tests before each dose vaccination. * nonchildbearing potential is defined as surgically sterile (history of bilateral tubal ligation, bilateral oophorectomy, hysterectomy) or postmenopausal. a follicle-stimulating hormone (fsh) level and the amenorrhea duration (e.g. amenorrhea for ≥ 12 consecutive months prior to screening without an alternative medical cause) may be measured at the discretion of investigator to confirm postmenopausal status. * the effective contraceptive methods include sexual abstinence or adequate contraceptive measures such as intrauterine or implanted contraceptive device, oral contraceptives, injected or implanted contraceptives, sustained-release topical contraceptives, condoms (male), diaphragm, and cervical cap, etc. 6. males participating in this study who are involved in heterosexual sexual activity must agree to practice adequate contraception (as described above) and refrain from donating sperm until 90 days after receiving the final dose vaccination. 7. agreement to refrain from blood donation during the study. 8. provide written informed consent form (icf) prior to study enrollment.

inclusion criteria: 1. aged 18 years and older. 2. able and willing to comply with all study requirements. 3. willing to allow investigators to discuss the medical history with his/her general practitioner/personal doctors and access all medical records which are relevant to study procedures. 4. healthy adults, or adults with stable medical condition who have a pre-existing medical condition that does not meet any exclusion criteria. a stable medical condition is defined as disease not requiring significant change in therapy or hospitalization for worsening disease during the 3 months before enrollment. 5. for females of childbearing potential only, willing to practice continuous effective contraception until 90 days after the final dose vaccination, and have negative pregnancy tests before each dose vaccination. * nonchildbearing potential is defined as surgically sterile (history of bilateral tubal ligation, bilateral oophorectomy, hysterectomy) or postmenopausal. a follicle-stimulating hormone (fsh) level and the amenorrhea duration (e.g. amenorrhea for ≥ 12 consecutive months prior to screening without an alternative medical cause) may be measured at the discretion of investigator to confirm postmenopausal status. * the effective contraceptive methods include sexual abstinence or adequate contraceptive measures such as intrauterine or implanted contraceptive device, oral contraceptives, injected or implanted contraceptives, sustained-release topical contraceptives, condoms (male), diaphragm, and cervical cap, etc. 6. males participating in this study who are involved in heterosexual sexual activity must agree to practice adequate contraception (as described above) and refrain from donating sperm until 90 days after receiving the final dose vaccination. 7. agreement to refrain from blood donation during the study. 8. provide written informed consent form (icf) prior to study enrollment.

inclusion criteria: aged 18 years and older. able and willing to comply with all study requirements. willing to allow investigators to discuss the medical history with his/her general practitioner/personal doctors and access all medical records which are relevant to study procedures. healthy adults, or adults with stable medical condition who have a pre-existing medical condition that does not meet any exclusion criteria. a stable medical condition is defined as disease not requiring significant change in therapy or hospitalization for worsening disease during the 3 months before enrollment. for females of childbearing potential only, willing to practice continuous effective contraception until 90 days after the final dose vaccination, and have negative pregnancy tests before each dose vaccination. nonchildbearing potential is defined as surgically sterile (history of bilateral tubal ligation, bilateral oophorectomy, hysterectomy) or postmenopausal. a follicle-stimulating hormone (fsh) level and the amenorrhea duration (e.g. amenorrhea for ≥ 12 consecutive months prior to screening without an alternative medical cause) may be measured at the discretion of investigator to confirm postmenopausal status. the effective contraceptive methods include sexual abstinence or adequate contraceptive measures such as intrauterine or implanted contraceptive device, oral contraceptives, injected or implanted contraceptives, sustained-release topical contraceptives, condoms (male), diaphragm, and cervical cap, etc. males participating in this study who are involved in heterosexual sexual activity must agree to practice adequate contraception (as described above) and refrain from donating sperm until 90 days after receiving the final dose vaccination. agreement to refrain from blood donation during the study. provide written informed consent form (icf) prior to study enrollment.

inclusion criteria: aged 18 years and older. able and willing to comply with all study requirements. willing to allow investigators to discuss the medical history with his/her general practitioner/personal doctors and access all medical records which are relevant to study procedures. healthy adults, or adults with stable medical condition who have a pre-existing medical condition that does not meet any exclusion criteria. a stable medical condition is defined as disease not requiring significant change in therapy or hospitalization for worsening disease during the 3 months before enrollment. for females of childbearing potential only, willing to practice continuous effective contraception until 90 days after the final dose vaccination, and have negative pregnancy tests before each dose vaccination. nonchildbearing potential is defined as surgically sterile (history of bilateral tubal ligation, bilateral oophorectomy, hysterectomy) or postmenopausal. a follicle-stimulating hormone (fsh) level and the amenorrhea duration (e.g. amenorrhea for ≥ 12 consecutive months prior to screening without an alternative medical cause) may be measured at the discretion of investigator to confirm postmenopausal status. the effective contraceptive methods include sexual abstinence or adequate contraceptive measures such as intrauterine or implanted contraceptive device, oral contraceptives, injected or implanted contraceptives, sustained-release topical contraceptives, condoms (male), diaphragm, and cervical cap, etc. males participating in this study who are involved in heterosexual sexual activity must agree to practice adequate contraception (as described above) and refrain from donating sperm until 90 days after receiving the final dose vaccination. agreement to refrain from blood donation during the study. provide written informed consent form (icf) prior to study enrollment.