Nasal spray vs. needle: which flu vaccine works better?

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

Inclusion Criteria: 1. Healthy individuals (Charlson´s co-morbidity index :0, and investigator judged as healthy) 2. Age: 18-49 years 3. Total IgG levels in normal range (discretion of investigator according to local lab) 4. Total IgA levels (discretion of investigator according to local lab) 5. Undetectable HAI titres to the H3N2 component of the vaccines\* 6. Normal CD4+ and CD8+ T-cell and normal B-cell counts 7. Reference levels from ISO-15189 accredited T-, B- and NK-cell count routine analyses will be applied. * If \<20% of the first 100 screened persons apply to this criterion, this will be changed to a specific cut off based on the lowest quartile level of HAI titres to the H3N2 component of these 100 screened persons. Exclusion Criteria: 1. Laboratory-confirmed influenza infection during the past year documented by a positive PCR test in the Danish Microbiological database or anamnestic reported influenza infection in the same period 2. Active smoker 3. BMI \> 35 kg/m2 4. Women of childbearing potential not using safe contraception, or who are pregnant, or breast-feeding 5. Any allergies to components of or contraindication for Vaxigriptetra® or Flumist® incl. previous severe adverse reactions to influenza vaccinations or components of the vaccines 6. Use of immunosuppressive drugs\* within the past 6 months or who are currently using them 7. HIV, HBV, HCV laboratory confirmed active infection at screening visit 8. Have an acute illness, including an oral temperature ≥ 38°C, within 3 days prior to vaccination 9. 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 10. Any known malignant neoplasm within 5 years (except basal carcinoma of the skin). 11. Severe mental illness or linguistic issues which significantly impedes cooperation 12. Inability to provide written informed consent * defined as: Azathioprin, methotrexate, cyclophosphamide, basiliximab, belimumab, anifrolumab, alemtuzumab, rituximab, mycophenolat, calcineurin inhibitors (ciclosporin, voclosporin and tacrolimus), mTOR inhibitors (everolimus and sirolimus), prednisolone (or any corticosteroid in doses above the equivalent of 5 mg prednisolone), TNF-α inhibitors (such as infliximab), anti-thymocyte globulin.