Assess the Safety and Immunogenicity of NDV-HXP-S Vaccine in Thailand

This study (GPO NDV-HXP-S) will be conducted in 2 phases. Phase 1 will evaluate the safety, tolerability and immunogenicity COVID-19 vaccine (NDV-HXP-S) administered at different doses levels (1, 3, and 10 µg) without adjuvant, and at two different dose levels (1 and 3 µg) with the adjuvant CpG 1018 among healthy adults, (age 18-59 years, 210 subjects). NDV-HXP-S or placebo (0.9% normal saline for injection) will administer IM according to a repeat vaccination schedule (given 28 days apart). In addition, as exploratory objectives, a total of 36 subjects will be randomly selected (1:1:1 ratio) from placebo and two high-dose groups i.e., NDV-HXP-S 10 µg and NDV-HXP-S 3 µg + CpG 1018, to provide additional blood at V1, V5 and V7 for assessment of T-cell-mediated immunity (CMI). An interim analysis of Phase 1 data will be conducted as the basis for decisions about advancement to Phase 2 of the study and about treatment group down selection. In the Phase 2 study, 250 subjects aged 18-75 years will be randomized (1:2:2) to placebo (0.9% normal saline for injection), or one of two selected formulations of NDV HXP S being evaluated in Phase 1 will be enrolled to Phase 2 study. Twelve subjects in each of the three Phase 2 groups (distributed among the two age strata) will be randomized to provide additional blood at V1, V5 and V7 for assessment of T-cell-mediated immunity (CMI). Unblinding will be done as per specific SOP provided by Sponsor. The PI will be expected to provide a rationale for the necessity of unblinding, based on the expectation that knowledge of the subject's treatment assignment will have a meaningful impact on the subject's medical care in the short term. If a subject's treatment assignment is unblinded, the subject will remain in the study and continue with protocol-defined study visits and procedures, unless there is another reason for subject discontinuation. Scheduled unblinding regarding safety concern during severe COVID-19 situation: The elderly subjects (60-75 years) who received placebo will be unblinded and discontinued as soon as COVID-19 vaccine (AstraZeneca) become available from Sponsor. If unblinding is occurred before complete enrollment of 75 elderly subjects, the randomization assignment will be skipped in placebo arm. Therefore, no further subjects will be randomly assigned to receive placebo after unblinding.