A Study of APL-10456-Vaccine

Inclusion Criteria: * Age Part A: Age ≥18 years and ≤54 years Part B: Age ≥55 years * Healthy participants who are determined by medical history, physical examination, and clinical judgment of the investigator to be eligible for inclusion in the study. Exclusion Criteria: * History of severe allergic or anaphylactic reactions of any type * Acutely ill or febrile (temperature ≥38.0°C/100.4°F) 72 hours prior to or at the Day 1 visit * History or presence of clinically significant cardiovascular, pulmonary, hepatic, renal, haematological, gastrointestinal, endocrine, immunologic, dermatologic, psychiatric or neurological disease/disorder within the past 3 months, or any acute minor illness (e.g. common cold, influenza, minor infection) within the past 1 month, determined by the PI (or delegate) to be clinically relevant * Reported history of congenital or acquired immunodeficiency * Dermatologic conditions that could affect local solicited AR assessments * Coagulopathy or a bleeding disorder that is considered a contraindication to IM injection or phlebotomy * Diagnosis of a malignancy within previous 5 years * Has received systemic immunosuppressants for \>14 days in total within 180 days prior to the Randomization Visit * Has received or plans to receive any licensed or authorized vaccine, including COVID-19 vaccines, ≤28 days prior to the study injection (Day 1) or plans to receive a licensed or authorized vaccine within 28 days after the final study injection * Has received systemic immunoglobulins, long-acting biological therapies that affect immune responses (eg, infliximab), or blood products within 90 days prior to the Randomization Visit or plans to receive them during the study * Female participant with positive pregnancy test or Lactating females * Has positive serology tests result (HIV, HCV and HBsAg) at screening visit * Has positive drugs of abuse test results at screening visit * Has participated in an interventional clinical study within 3 months prior to the Randomization Visit or plans to do so while participating in this study * Has donated ≥450 mL of blood products within 28 days prior to the Randomization Visit or plans to donate blood products during the study