Assess the Safety and Immunogenicity of One or Two Doses of Sing2016 M2SR H3N2 Influenza Vaccine

Inclusion Criteria: 1\. Participant is a male or female child aged 6 months to 17 years inclusive at time of enrollment (each cohort has its own age upper and lower limits\*) * Cohort 1: 9-17 years (on or after the ninth birthday and before the eighteenth birthday at the time of the first dose); Cohorts 2, 3, and 4: 2-8 years (on or after the second birthday and before the ninth birthday at the time of the first dose); Cohorts 5, 6, and 7: 6 months to 23 months (on or after the sixth month of life based on calendar day and before the second birthday at the time of the first dose) 2. For Cohorts 1 to 4, receipt of at least 2 doses of seasonal influenza vaccine in the past. 3\. For Cohorts 5 to 7, receipt of no seasonal influenza vaccines in the past and no documented history of laboratory-confirmed influenza illness 4. Parent/guardian of the participating child provides written informed permission and participating child provides assent\* prior to initiation of any study procedures * As appropriate by age or development and approved by the Institutional Review Board (IRB) 5. Parent/guardian and participant, as appropriate, are able to understand and comply with planned study procedures and are available for all study visits 6. Participant is in good health as assessed by the principal investigator or other designated study investigator\* * Based on medical history and physical examination (physical examination may be done as part of routine medical care or specifically for eligibility screening) 7. Parent/guardian of the participating child agrees not to allow the participant to join another clinical trial that includes an investigational agent or device during the study period 8. A female participant of child-bearing potential\* agrees to abstain from sexual intercourse or to correctly use an acceptable method of contraception\*\* * A female of child-bearing potential is defined as a female who is post-menarchal and not sterilized via tubal ligation, bilateral oophorectomy, salpingectomy, hysterectomy, or successful Essure (R) placement (permanent, non-surgical, non-hormonal sterilization) with documented radiological confirmation test at least 90 days after the procedure. This applies only to participants in Cohort 1. \*\*Acceptable methods of contraception must be used from 30 days prior to vaccination until 60 days after the last study vaccination (not Inactivated Influenza Vaccine (IIV4)) and include full abstinence from sexual intercourse with a male partner, monogamous relationship with vasectomized partner who has been vasectomized for 180 days or more or shown to be azoospermic prior to the participant receiving the study vaccination, barrier methods such as condoms or diaphragms/cervical cap, intrauterine devices, NuvaRing (R), and licensed hormonal methods such as implants, injectables, or oral contraceptives ("the pill"). 9\. A female participant of child-bearing potential must have a negative urine pregnancy test within 24 hours prior to each study product 10. A male who is sexually active with a female of childbearing potential must agree to use an acceptable method of contraception\* * From the time of the first dose of study vaccine until 60 days after receipt of the last dose study vaccine, only in cohort 1. The only acceptable method of contraception for males who are sexually active with females of childbearing potential is condoms. Exclusion Criteria: 1. Has a body temperature of 38 degrees Celsius or 100.4 degrees Fahrenheit (oral or axillary) or greater or another acute illness\* within the 72 hours prior to study vaccination \*Potential participants who are recovering from an acute illness and have residual minimal symptoms, which, in the opinion of the site principal investigator or appropriate sub-investigator, will not likely affect the evaluation of outcome measures are not ineligible. Temperature evaluation will not be performed as a study procedure on participants prior to administration of seasonal influenza vaccine 2. Has any medical or mental health disease or condition\* that would render study participation unsafe, or would interfere with the evaluation of the responses \*In the opinion of the site principal investigator or appropriate sub-investigator 3. Has a history of provider-diagnosed asthma requiring the use of medications at any age or has had a wheezing episode or use of medications to treat asthma in the 12 months prior to screening. 4. Has immunosuppression as a result of an underlying illness or treatment, a recent history or current use of immunosuppressive or immunomodulating disease therapy 5. Has a diagnosis of or history of malignant neoplastic disease 6. Has taken oral, parenteral (intramuscular or intravenous), inhaled, or nasal corticosteroids of any dose within 30 days prior to study vaccination 7. Has known HIV, hepatitis B, or hepatitis C infection 8. Has known hypersensitivity or allergy to any components of the study vaccine or material in the nasal delivery device\* \*Vaccine components: sucrose, sodium chloride, phosphate, glutamate; delivery device material: polycarbonate, polypropylene, synthetic rubber 9. Has a history of severe reactions following previous immunization with licensed or unlicensed influenza vaccines 10. Has a history of an anatomic disorder of the nares or nasopharynx 11. Has a history of chronic sinus infections 12. Has a history of or currently smokes or vapes 13. Has a history of Guillain-Barré syndrome 14. Use of aspirin- or salicylate-containing products in the 30 days prior to or intends to use these products in the 30 days following administration of the investigational vaccine 15. Has a history of documented influenza or receipt of influenza antiviral treatment in the 4 months prior to the first vaccination 16. Receipt of any antiviral drug within the week prior to or following the investigational vaccine. 17. Receipt of a licensed live vaccine within 30 days prior to the first study vaccination or plans to receive a licensed live vaccine within the 30 days after the last study vaccination. 18. Receipt of licensed inactivated non-influenza vaccine within 14 days prior to the first study vaccination, or plans to receive licensed, inactivated vaccine within the 30 days after the last study vaccination. \*\* Participants will be asked to avoid receipt of any routine licensed vaccines or vaccines under emergency use authorization during the periods described. 19. Receipt of an influenza vaccine within the 4 months prior to the first study vaccination or plans to receive an influenza vaccine following the last study vaccination. Seasonal IIV4 will be received by participants as part of this trial. 20. Receipt of immunoglobulin or other blood products within the 6 months prior to the first study vaccination or plans to receive during the period of study participation. 21. Receipt of an experimental\* agent or device within the 6 months prior to the first study vaccination or expects to receive an experimental agent or device during the study period. \*Products for treatment or prevention of coronavirus disease 2019 (COVID-19), when received under Emergency Use Authorization (EUA) or full FDA approval and not as part of a clinical trial, will not be deemed "experimental" for the purposes of this criterion and will not make an otherwise eligible prospective participant ineligible. 22. Is a family member of study personnel or personnel directly involved in the conduct or monitoring of the study. 23. Receipt of an approved or experimental product for treatment or prevention of COVID-19 within the 10 days prior to study enrollment. * Participants may enroll if greater than 10 days after receipt of the COVID-19 treatment or prevention. * Participants who are receiving COVID-19 vaccines around the time of dosing of the investigational product will be asked to avoid COVID-19 vaccination within the 10 days before any vaccination in the study and within any reactogenicity period (the day of and 7 days following each intranasal vaccination). 24. Inability of the study team to collect 5 mL of blood from the participant before the first vaccination (pre-vaccination blood).