Cellular and humoral immune responses before and after seasonal influenza vaccination will be assessed. Each year, up to 100 participants will be enrolled. To study age-specific differences in immune responses, participants with various years of birth will be enrolled. The investigators hypothesize that humans with different birth years will mount antibody and cellular responses of different specificities following seasonal influenza vaccination.

The investigators and others have shown that the first influenza virus someone is exposed to leaves an immunological imprint that affects antibody responses to antigenically related influenza strains later in life. Year of birth can be used to predict influenza virus exposures during the first years of life. It is possible that immune responses to influenza vaccination later in life differ between people with different birth years, depending on what virus someone was "imprinted" with. This could result in birth year differences in antibody responses upon vaccination and vaccine effectiveness. However, the effect of year of birth on the specificity of humoral and cellular immune responses elicited by influenza vaccination has not been studied in depth. In this study, the investigators will measure influenza virus cellular and humoral immune responses in individuals of different birth years before and after influenza vaccination.

Inclusion Criteria:

1. Provision of signed and dated informed consent form
2. Stated willingness to comply with all study procedures and availability for all study visits
3. Aged 18 years and older
4. In good health based on self-reported medical conditions via an online survey

Exclusion Criteria:

1. Known allergic reactions to components of the study vaccine
2. Known latex allergy
3. History of severe reactions following previous immunization with licensed or unlicensed influenza virus vaccines
4. History of GBS within 6 weeks of receipt of a previous influenza vaccine
5. Immunosuppression as a result of an underlying illness or treatment with immunosuppressive or cytotoxic drugs, or use of anticancer chemotherapy or radiation therapy within the preceding 36 months
6. Treatment with immunoglobulin or another blood product within the 3 months prior to enrollment in this study
7. Active neoplastic disease (excluding non-melanoma skin cancer or prostate cancer that is stable in the absence of therapy) or a history of any hematological malignancy ("active" is defined as having received treatment within the past 5 years)
8. Long-term (greater than 2 weeks) usage of oral or parenteral steroids, or high-dose inhaled steroids
9. Administration of an influenza vaccine within 2 months prior to enrollment
10. Known acute or chronic medical condition that, in the opinion of the investigator or appropriate sub-investigator, would render vaccination unsafe or would interfere with the evaluation of responses
11. Participation in a study that involves an experimental agent or having received an experimental agent (other than a COVID-19 vaccine) within 1 month prior to enrollment or expecting to receive another experimental agent during the study period
12. Intends to donate blood during the study period
13. Any condition that would, in the opinion of the site investigator, place the subject at an unacceptable risk of injury or render the subject unable to meet the requirements of the protocol
14. Pregnancy
15. Known human immunodeficiency virus, hepatitis B, or hepatitis C infection
16. Any condition that the principal investigator believes may interfere with successful completion of the study

Protocol and statistical analysis plan may need to be shared for publication.

At publication

Per journal publication policy