Inclusion Criteria:

* Documented informed consent of the participant
* Age \>=18 years
* Eastern Cooperative Oncology Group (ECOG) =\<1
* Allogeneic or autologous hematopoietic cell transplant (HCT), cellular therapy (chimeric antigen receptor \[CAR\] T-cell) recipients who are at \>= 3 months of infusion date of respective regimen
* Platelets \>= 50,000/mm\^3 (to be performed within 30 days prior to day 0 of protocol therapy unless otherwise stated)
* White blood cells (WBCs) \>= 1000/mm\^3 (to be performed within 30 days prior to day 0 of protocol therapy unless otherwise stated)
* Total bilirubin \< 1.5 X upper limit of normal (ULN) (to be performed within 30 days prior to day 0 of protocol therapy unless otherwise stated)
* Aspartate aminotransferase (AST) \< 2.5 X ULN (to be performed within 30 days prior to day 0 of protocol therapy unless otherwise stated)
* Alanine aminotransferase (ALT) \< 2.5 X ULN (to be performed within 30 days prior to day 0 of protocol therapy unless otherwise stated)
* Creatinine \< 1.5 X ULN (to be performed within 30 days prior to day 0 of protocol therapy unless otherwise stated)
* Negative COVID-19 PCR test
* Women of childbearing potential (WOCBP): negative urine or serum pregnancy test (to be performed within 30 days prior to day 0 of protocol therapy unless otherwise stated). If the urine pregnancy test is inconclusive a serum pregnancy test will be required
* Agreement by females and males of childbearing potential\* to use an effective method of birth control or abstain from heterosexual activity for the course of the study through at least 6 weeks after the last dose of protocol therapy

* Childbearing potential defined as not being surgically sterilized (men and women) or have not been free from menses for \> 1 year (women only)

Exclusion Criteria:

* Systemic corticosteroids required for chronic conditions at doses \> 0.5mg/kg/day prednisone equivalent within 7 days of enrollment
* Prior Evusheld or other anti-SARS CoV-2 prophylaxis \< 2 weeks prior to enrollment
* Therapies that cause profound T-cell or B cell depletion within 30 days of enrollment
* Maintenance therapies (e.g. rituximab, Bruton tyrosine kinase inhibitors, Janus kinase inhibitors) within 30 days of enrollment
* Received investigational or licensed SARS-CoV-2 vaccines after their qualifying cellular therapy. Patients who received a SARS- CoV-2 vaccine prior to cellular therapy are eligible for this trial, as revaccination for these patients (e.g. flu and shingles vaccine) is standard of care.
* Received a live vaccine ≤30 days prior to administration of study vaccine or subjects who are =\< 2 weeks within administration of inactivated vaccines (e.g. influenza vaccine). Flu shots are allowed \> 2 weeks before the first injection and \> 2 weeks post 2nd injection
* History of allergic reactions attributed to compounds of similar chemical or biologic composition to vaccine agents
* History of adverse event with a prior smallpox vaccination
* Any MVA vaccine or poxvirus vaccine in the last 12 months
* History (suspected or confirmed) of myocarditis or pericarditis
* Clinically significant uncontrolled illness
* Females only: Pregnant or breastfeeding
* Any other condition that would, in the Investigator's judgment, contraindicate the subject's participation in the clinical study due to safety concerns with clinical study procedures
* Prospective participants who, in the opinion of the investigator, may not be able to comply with all study procedures (including compliance issues related to feasibility/logistics)
* Anyone considered to be in a vulnerable population as defined in 45 CFR §46.111 (a)(3) and 45 CFR §46, Subparts B-D