GEneRating Mucosal Immunity After INfluenzA Infection and Vaccination in Lung and Lymphoid TissuE

Inclusion Criteria:

• Adults aged between 18-40 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.