Scientists to compare nasal flu vaccine with real flu infection in healthy volunteers

Copied word for word from the study's registry entry, so the wording is the study team's rather than ours.

Inclusion Criteria: * Adults aged between 18-55 years inclusive * Sero-suitable as defined by a serum micro-neutralisation titre \<1:20 * Female participant who is not of child-bearing potential as assessed by an investigator OR is willing and able to use contraception as described in the protocol * Male participants who are willing to use one of the contraception methods described in the protocol * In good health with no clinically significant medical conditions Exclusion Criteria * History of clinically significant/currently active conditions; * Cardiovascular, thromboembolic/cerebrovascular disease. * Types of chronic respiratory disease in adulthood. * Significant wheeze in the past * Respiratory symptoms including wheeze, resulting in hospitalisation * Known bronchial hyperactivity to viruses * Diabetes mellitus * Migraine with associated symptoms like hemiplegia/vision loss. Cluster headache/migraine/prophylactic treatment for migraine. * History of autoimmune disease/known immunodeficiency of any cause * Immunosuppression. * Known coagulation disorder/anticoagulant therapy * Psychiatric illness including participants with a history of depression and/or anxiety with associated psychiatric comorbidities * Other major disease that, under the PI's discretion, could interfere with the participant completing the study. * Concurrent serious illness including history of malignancy that could interfere with the study or a participant completing the study. * Known IgA deficiency/immotile cilia syndrome/Kartagener's syndrome * Significant abnormality altering the anatomy/function of the nose or nasopharynx, a clinically significant history of epistaxis within the last 3 months, nasal/sinus surgery within 6 months of Day 0, including nasopharyngeal malignancy, arterio-venous malformation, or undiagnosed nasopharyngeal mass * Inhaled bronchodilator/inhaled steroid use within the last 12 months before Day 0 * Acute upper respiratory tract infection in the past 6 weeks. * Receipt of systemic glucocorticoids (in a dose ≥ 5 mg prednisone daily or equivalent) within one month, or any other cytotoxic or immunosuppressive drug within 6 months before Day 0 * Receipt of any vaccine within 30 days of Day -14 * Any significant medical condition/prescribed drug, under the PI's discretion * Presence of cold-like symptoms and/or fever on Day -14 or Day 0. * Receipt of blood/blood products/loss (including blood donations) of 550 mL or more of blood during the 3 months prior to Day -14. * Significant history/presence of drug/alcohol misuse by self-report. * Current use of drugs through nose inhalation or inhaled route including recreational drugs. * Regular smoking and/or vaping and/or using nicotine-containing products in the past 3 months OR \>5 pack-year lifetime history by self-report (5 pack years is equivalent to one pack of 20 cigarettes per day for 5 years). * History of anaphylaxis and/or a history of severe allergic reaction or significant intolerance to any food/drug, as assessed by the PI. * Clinically active rhinitis (including hay fever)/history of moderate to severe rhinitis/history of seasonal allergic rhinitis likely to be active at the time of inclusion into the study and/or requiring regular nasal corticosteroids on an at least weekly basis, within 30 days of enrolment. * Anyone with any of the following contraindications to receiving the Fluenz Tetra Vaccine: * Allergy to gentamicin, gelatin or the other ingredients of the fluenz vaccine.