Primary Study Objective: To evaluate the safety and tolerability profile of two dose levels of the NDV-HXP-S vaccine as an IN, IM, or a combined administration IN+IM to healthy, previously immunized adults up to 14 days after administration.~Secondary Study Objective: To evaluate the safety and tolerability profile of two dose levels of the NDV-HXP-S vaccine as an IN, IM, or a combined administration IN+IM to healthy, previously immunized adults up to 365 days after administration.
This study will be a phase-1, open-label, placebo-controlled, evaluation of two-dosages of a live, recombinant Newcastle disease virus expressing the spike protein of SARS-CoV-2 (NDV-HXP-S), an investigational product for IN, IM, or a combined IN+IM vaccination in healthy adults previously immunized against COVID-19. The IN and IM live virus vaccinations will be identical in composition and only differ in route of administration.