Vaccine Pandemic Preparedness Through Airway Immunological Characterization (VAXXAIR)

Inclusion Criteria: Participants who have not received any influenza vaccines as per medical history and documented in The Danish Vaccine Registry(DDV) Exclusion Criteria: Laboratory-confirmed influenza infection during the past year documented by a positive PCR test in the Danish Microbiological database Total IgG levels < 6.1 g/L obtaining at screening visit Influenza specific IgA in upper quartile in mucosa. Upper quartile will be defined "real time" in the screening population Active smoker BMI > 35 Charlson (score > 0) Women of childbearing potential not using safe contraception, or who are pregnant, or breast-feeding Any allergies to components of or contraindication for Vaxigriptetra® or Flumist® Participants who have experienced severe adverse reactions to previous influenza vaccinations or components of the vaccines, including allergy to egg Use of immunosuppressive drugs1 within the past 6 months or who are currently using them Known immunodeficiency disorders [any diagnosis that would qualify to an ICD-10 diagnosis in the categories DD80-DD89 (except DD86) HIV, HBV, HCV laboatory confirm active infection at screening visit Have an acute illness, including an oral temperature ≥ 38°C, within 3 days prior to vaccination Have received any vaccines, including live-attenuated vaccines within 4 weeks before inclusion, or plan receipt of such vaccines within 30 days following the inclusion Any known malignant neoplasm within 5 years (except basal carcinoma of the skin). Severe mental illness or linguistic issues which significantly impedes cooperation Inability to provide written informed consent Previous medical history, evidence of an intercurrent illness or any condition that, in the opinion of the investigator, would interfere with evaluation of the study vaccine products or interpretation of subject safety or that may compromise the safety of the subject in the study.