Phase 3 Trial of Serbian Seasonal Influenza Vaccine

Inclusion Criteria: * Aged 18 to 65 years on the day of screening/enrollment. * Literate (by self-report) and willing to provide written informed consent. * Able to attend all scheduled visits and to comply with all trial procedures. * Healthy or medically stable, as established by medical history and physical examination. For individuals with medical conditions, symptoms/signs, if present must be stable under control or unchanged for the past three months. If medication is used to treat the condition, the medication dose must have been stable for at least one month preceding vaccination. For female participants: * Not breast feeding, non-pregnant (based on negative urine pregnancy test) and no plan to become pregnant up to Day 22. * Women who are not surgically sterile (hysterectomy or tubal ligation) or post-menopausal for more than one year must be willing to use effective contraceptive method to prevent pregnancy until three weeks (Day 22) after vaccination. Effective methods include intrauterine device, hormonal contraceptives (oral, injectable, patch, implant, ring) or double barrier contraceptives (condom or diaphragm with spermicide). Women with credible history of abstinence may be enrolled at the discretion of the investigator. Exclusion Criteria: * Participation in another clinical trial involving any therapy within the previous three months or planned enrollment in such a trial during the period of this study. * Receipt of influenza vaccine in the last 10 months. * Receipt of any non-study vaccine within four weeks prior to enrollment or refusal to postpone receipt of such vaccines until after the Day 22 visit. * Receipt of immune globulin or other blood products within three months prior to study enrollment or planned receipt of such products prior to the Day 22 visit. * Known or suspected congenital or acquired immunodeficiency. * Chronic administration (defined as more than 14 consecutively-prescribed days) of immunosuppressants or other immune-modulating therapy within six months prior to study enrollment. (For corticosteroids, this means prednisone or equivalent, ≥ 0.5 mg per kg per day; topical steroids are allowed.) * Unstable illness by history or physical examination that in the opinion of the investigator, might interfere with the conduct or results of the study or pose additional risk to the participant. * Hypersensitivity after previous administration of any vaccine. * Suspected or known hypersensitivity to any of the study vaccine components, including chicken or egg protein or antibiotics. * Bleeding disorder or receipt of anticoagulants in the three weeks preceding enrollment. * Known active tuberculosis or symptoms of active tuberculosis, regardless of cause (self-report). * Current alcohol or drug addiction that in the opinion of the Investigator, might interfere with the ability to comply with trial procedures. * History of Guillain-Barré Syndrome. * Neoplastic disease or any hematologic malignancy. Allowed: localized skin or prostate cancer that is no longer being treated and is stable at the time of vaccination and participants who have a history of neoplastic disease and who have been disease free for ≥ 5 years. * Any condition that, in the opinion of the investigator, would increase the health risk to the participant if he/she participates in the study, or would interfere with the evaluation of the study objectives.