T-cell And General Immune Response to Seasonal Influenza Vaccine (SLVP018) Year 5, 2013

Inclusion Criteria:

   1. Otherwise healthy, twin children age 1-8 years (identical or fraternal twin pairs)

   2. Parent willing to sign the informed consent form and child willing to sign assent if
   indicated.

   3. Availability for follow-up for the planned duration of the study at least 28 days
   after last immunization.

   4. Acceptable relevant medical history and vital signs.

Exclusion Criteria:

   1. Prior off-study vaccination with trivalent inactivated influenza vaccine (IIV3) or
   live attenuated influenza vaccine (LAIV) in Fall 2013

   2. Allergy to egg or egg products, or to vaccine components or thimerosal (if IIV3
   multidose vials used)

   3. Life-threatening reactions to previous influenza vaccinations

   4. Active systemic or serious concurrent illness, including febrile illness on the day of
   vaccination

   5. History of immunodeficiency (including HIV infection)

   6. Known or suspected impairment of immunologic function, including, but not limited to,
   clinically significant liver disease, diabetes mellitus treated with insulin, moderate
   to severe renal disease or any other chronic disorder which, in the opinion of the
   investigator, might jeopardize volunteer safety or compliance with the protocol.

   7. Chronic Hepatitis B or C

   8. Recent or current use of immunosuppressive medication, including glucocorticoids
   (corticosteroid nasal sprays, topical steroids are permissible). History of any
   cancer.

   9. Autoimmune disease including rheumatoid arthritis treated with immunosuppressive
   medication such as Plaquenil, methotrexate, prednisone, Enbrel) which, in the opinion
   of the investigator, might jeopardize volunteer safety or compliance with the
   protocol.

10. History of blood dyscrasias, or hemoglobinopathies requiring regular medical follow up
   or hospitalization during the preceding year

11. Use of any anti-coagulation medication such as Coumadin or Lovenox, or anti-platelet
   agents such as aspirin.

12. Receipt of blood or blood products within the past 6 months or planned receipt of
   blood products prior to completion of study visits.

13. Medical or psychiatric condition or occupational responsibilities that preclude
   participant compliance with the protocol

14. Receipt of inactivated vaccine 14 days prior to enrollment, or planned non-study
   vaccination prior to completion of Visit 03 or 04 (~Day 28 after the last study
   vaccination)

15. Receipt of a live, attenuated vaccine within 30 days prior to first vaccination, or
   planned immunization with a live, attenuated vaccine before completion of study visits
   (inform study staff of any non-study vaccinations received during the study period).

16. Need for allergy immunization (that cannot be postponed) during the study period.

17. History of Guillain-Barre Syndrome

18. Use of investigational agents within 30 days prior to enrollment or planned use of
   investigational agents prior to completion of study visits.

19. Any condition which, in the opinion of the investigator, might interfere with
   volunteer safety, study objectives or the ability of the participant to understand or
   comply with the study protocol.