• Individuals ≥18 years and \<30 years of age at the time of consent.

• Willing and able to comply with all scheduled visits, vaccination plan, laboratory tests and other trial procedures.

• Determined by medical history, complete physical examination and clinical judgement of the investigator to be in good state of health\*.

⁃ As determined by medical history and physical examination to evaluate acute or ongoing chronic medical diagnoses/conditions that have been present for at least 90 days, which would affect the safety assessment of subjects. Chronic medical diagnoses/conditions should be stable for the last 60 days (no hospitalizations, emergency room (ER), or urgent care for condition or need for supplemental oxygen). This includes no change in chronic prescription medication, dose, or frequency due to deterioration of the chronic medical diagnosis/condition in the 60 days before enrollment. Any prescription change that is due to change of health care provider, insurance company, etc., or done for financial reasons, and in the same class of medication, will not be considered a deviation of this inclusion criterion.

‣ Any change in prescription medication due to improvement of a disease outcome, as determined by the participating site principal investigator (PI) or appropriate sub- investigator, will not be considered a deviation of this inclusion criterion. Subjects may be on chronic or as needed (prn) medications if, in the opinion of the participating site PI or appropriate sub-investigator, they pose no additional risk to subject safety or assessment of reactogenicity and immunogenicity, and do not indicate a worsening of medical diagnosis/condition. Similarly, medication changes subsequent to enrollment and trial vaccination are acceptable provided the change was not precipitated by deterioration in the chronic medical condition, and there is no anticipated additional risk to the subject or interference with the evaluation of responses to trial vaccination.

• Prior receipt of two doses of mumps vaccine in childhood (as MMR or MMRV).

• Women of childbearing potential\* must agree to use or have practiced true abstinence\*\* or use at least one acceptable primary form of contraception.\*\*\*, \*\*\*\* Note: These criteria are applicable to females in a heterosexual relationship and child-bearing potential (i.e., the criteria do not apply to subjects in a same sex relationship).

• \*Not of childbearing potential: post-menopausal females (defined as having a history of amenorrhea for at least one year) or a documented status as being surgically sterile (hysterectomy, bilateral oophorectomy, tubal ligation/salpingectomy, or Essure® placement).

• \*\*True abstinence is no sexual intercourse 100% of the time (i.e. male's penis never enters the female's vagina). Periodic abstinence (e.g., calendar, ovulation, symptothermal, post- ovulation methods) and withdrawal are not acceptable methods of contraception.

• \*\*\*Acceptable forms of primary contraception include monogamous relationship with a vasectomized partner who has been vasectomized for 180 days or more prior to the subject's vaccination, intrauterine devices, birth control pills, and injectable/implantable/insertable hormonal birth control products, condom, or diaphragm with spermicide. If barrier methods are to be used, then double barrier methods of protection are required, i.e. male condom, in combination with a cap, diaphragm, or sponge with spermicide.

• \*\*\*\*Must use at least one acceptable primary form of contraception for at least 28 days prior to vaccination and at least one acceptable primary form of contraception for 90 days after last vaccination. If barrier methods are to be used, then double barrier methods of protection are required, i.e. male condom, in combination with a cap, diaphragm, or sponge with spermicide.

• Women of childbearing potential must have a negative urine or serum pregnancy test within 24 hours prior to vaccination.

• Male subjects of childbearing potential\* must use condoms to ensure effective contraception with a female partner of childbearing potential from vaccination until 90 days after vaccination. Such female partners must also use an acceptable form of primary contraception as described under inclusion criterion #5. If barrier methods are to be used, then double barrier methods of protection are required, i.e. male condom, in combination with a cap, diaphragm, or sponge with spermicide.

• \*Biological males who are post-pubertal and considered fertile until permanently sterile by bilateral orchiectomy or vasectomy.

• Female subjects agree to refrain from egg donation from time of vaccination until 90 days after vaccination.

• Male subjects agree to refrain from sperm donation from the time of vaccination until 90 days after vaccination.