A Study to Evaluate the Safety and Immunogenicity of Two Doses of DCVC H1 HA mRNA-LNP in Healthy Adults

Inclusion Criteria:

1. Provide written informed consent prior to initiation of any study procedure.

2. Are able to understand and comply with planned study procedures and be available forall study visits.

3. Are males or non-pregnant, non-breastfeeding females, 18 to 49 years of age,inclusive at time of enrollment.

4. Must agree to collection of venous blood and nasal absorption specimens per protocoland enrollment in DMID 19-0025 biorepository protocol for use of residual bloodspecimens.

5. Are in good health* and not have clinically significant medical, psychiatric,chronic or intermittent health conditions including those listed in ExclusionCriteria (Section 5.3) *Refer to the protocol specific Manual of Procedures (Section 4.3) for this definition.

6. Does not have an ongoing symptomatic condition* for which participant has had or hasongoing medical investigations but has not yet received a diagnosis or treatmentplan.

*e.g., ongoing fatigue without a diagnosis for symptom.

7. Pulse is 50 to 100 beats per minute, inclusive.

8. Systolic blood pressure is 90 to 139 mmHg, inclusive.

9. Diastolic blood pressure is 55 to 89 mmHg, inclusive.

10. Body mass index (BMI) of 18 kilograms/square meter (kg/m^2) to <35 kg/m^2 (inclusive) and weight >/=110 lbs. at screening.

11. Women of childbearing potential* must agree to use or have practiced true abstinenceor use at least 1 acceptable primary form of contraception. **

• Not of child bearing potential - post-menopausal females (defined as having ahistory of amenorrhea for at least one year) or a documented status as beingsurgically sterile (hysterectomy, bilateral oophorectomy, salpingectomy, orEssure placement with history of documented radiological confirmation test atleast 90 days after the procedure)

• True abstinence is 100% of time no sexual intercourse (male's penis enters thefemale's vagina). (Periodic abstinence [e.g. calendar, ovulation,symptothermal, post-ovulation methods] and withdrawal are not acceptablemethods of contraception).

• Acceptable forms of primary contraception include monogamous relationship witha vasectomized partner who has been vasectomized for 180 days or more prior tothe participant receiving the study product, tubal ligation, intrauterinedevices, birth control pills, and injectable/implantable/insertable hormonalbirth control products.

• Must use at least one acceptable primary form of contraception or trueabstinence for at least 30 days prior to receipt of study product and at leastone acceptable primary form of contraception or true abstinence for at least 30days following receipt of study product.

12. Women of childbearing potential* must have a negative serum pregnancy test atscreening and a negative urine pregnancy test within 24 hours prior to each studyvaccination.

13. Male participants receiving DCVC H1 HA mRNA Vaccine must agree to refrain fromdonating sperm and to use contraception until day 90 after last vaccination. **

• Acceptable contraception includes abstinence from intercourse with a female ofchildbearing potential or use of a male condom when engaging in any activitythat allows for passage of ejaculate to a female during the intervention periodfor at least 90 days after last study vaccination.

• Males in the immunogenicity comparator group do not have to refrain from spermdonation or abstain from intercourse or agree to use a male condom for purposesof this study.

Exclusion Criteria:

1. Have an acute illness* or fever (body temperature >/= 38.0°C/100.4°F), as determinedby the site PI or appropriate sub-investigator, within 72 hours prior to studyvaccination.

*An acute illness which is nearly resolved with only minor residual symptomsremaining is allowable if, in the opinion of the site PI or appropriatesub-investigator, the residual symptoms will not interfere with the ability toassess safety parameters as required by the protocol.

2. Have any medical disease or condition that, in the opinion of the site PI orappropriate sub-investigator, is a contraindication to study participation. **

• Including acute, subacute, intermittent or chronic medical disease or conditionthat would place the participant at an unacceptable risk of injury, render theparticipant unable to meet the requirements of the protocol, or may interfere withthe evaluation of responses or the participant's successful completion of thistrial.

3. Has a screening laboratory* > Grade 1.

*White blood cell count, absolute neutrophil count, absolute lymphocyte count,hemoglobin, platelet count, prothrombin time (PT), activated partial thromboplastintime (APTT), fibrinogen, creatinine, alanine aminotransferase, aspartateaminotransferase, alkaline phosphatase, total bilirubin, lipase

4. Has a positive urine toxicology screen (i.e., non-prescribed amphetamines, cocaine,and opiates).

5. ECG is deemed to be clinically significant* by the PI or appropriatesub-investigator.

*ECG consistent with probable or possible myocarditis/pericarditis or demonstratesclinically relevant abnormalities that may affect participant safety orinterpretation of study results. An ECG that shows an average QTcF (Fridericia'scorrection) interval >450 msec, complete left bundle branch block, signs of an acuteor indeterminate-age myocardial infarction, ST-T interval changes suggestive ofmyocardial ischemia, second- or third-degree AV block, or serious bradyarrhythmiasor tachyarrhythmias.

6. Troponin (Troponin T, High Sensitivity) outside the laboratory normal range atscreening.

7. Have any known or suspected immunosuppressive condition, acquired or congenital, orautoimmune conditions as determined by history and/or physical examination.

8. Have immunosuppression resulting from any treatment including a recent history (within 6 months prior to administration of study vaccine) or use ofimmunosuppressive or immune-modifying drugs.

9. Use of anticancer chemotherapy or radiation therapy (cytotoxic) within 3 years priorto study vaccination.

10. Have known active or recently active (12 months) neoplastic disease or a history ofany hematologic malignancy. Non-melanoma, treated, skin cancers are permitted.

11. Have known human immunodeficiency virus, hepatitis B or hepatitis C infection atscreening.

12. Have a positive test result for hepatitis B surface antigen, hepatitis C virusantibody, or human immunodeficiency virus types 1 or 2 antibodies at screening.

13. Have known chronic liver disease, including fatty liver disease.

14. Have known hypersensitivity or allergy to any components of the study vaccine (including polyethylene glycol or egg protein).

15. Have a history of a severe reaction including allergic reaction following previousimmunization with an investigational, authorized, or approved influenza vaccine ormRNA containing vaccine.

16. Have a history of Guillain-Barré Syndrome.

17. Have a known history of myocarditis, pericarditis, or myopericarditis.

18. Have a history of alcohol or drug abuse within 3 years prior to study vaccination.

19. Have any diagnosis, current or past, of schizophrenia, bipolar disease or otherpsychiatric diagnosis that may interfere* with participant compliance or safetyevaluations.

• As determined by the site PI or appropriate sub-investigator.

20. Have been hospitalized for psychiatric illness, history of suicide attempt, orconfinement for danger to self or others within 5 years prior to study vaccination.

21. Have taken oral or parenteral (including intra-articular) corticosteroids of anydose within 30 days prior to study vaccination. Intranasal or topical (skin or eyes)corticosteroids are permitted.

22. Have taken high-dose inhaled or nebulized corticosteroids* within 30 days prior tostudy vaccination.

• High-dose defined as per age as using inhaled high-dose per reference chart in theNational Heart, Lung and Blood Institute Guidelines for the Diagnosis and Managementof Asthma (EPR-3) or other lists published in UPTODATE

23. Have any significant disorder of coagulation requiring ongoing or intermittenttreatment.

24. Have received any approved or authorized vaccines other than seasonal influenzavaccine within 60 days before enrollment.

25. Have received seasonal influenza vaccine within the 90 days prior to enrollment.

26. Have a known history of documented influenza infection with the past 90 days.

27. Have a history of receipt of an investigational H1 influenza vaccine within the past 10 years.

28. Received immunoglobulin and/or any blood products (except Rho D immunoglobulin)within the 90 days prior to study vaccination.

29. Received an experimental agent* within 60 days prior to the study vaccination or areparticipating in another clinical trial with an interventional agent*.

• Including vaccine, drug, biologic, device, blood product, or medication.

• Including licensed or unlicensed vaccine, drug, biologic, device, bloodproduct, or medication.

30. The participant has any abnormality or permanent body art (eg, tattoo) that, in theopinion of the investigator, would obstruct the ability to observe local reactionsat the injection site.

31. Donation of blood or blood products within 30 days prior to dosing.

32. Has had significant exposure to someone with SARS-CoV-2 infection orlaboratory-confirmed influenza in the 14 days prior to screening or during theperiod between screening and enrollment visit*.

• Defined by the CDC as a close contact with someone who has COVID-19.

33. Has had a positive SARS-CoV-2 test (home or laboratory-based) within 14 days priorto the screening visit or during the period between screening and enrollment visits.