- patients who have received second allogeneic hct are not eligible (patients who have undergone a previous autologous hct are eligible - systemic corticosteroids required for chronic conditions at doses > 0.5mg/kg/day prednisone equivalent - patients on maintenance therapies (e.g. rituximab, bruton tyrosine kinase inhibitors, janus kinase inhibitors), who may have significantly attenuated response to vaccination - subjects using investigational or licensed agents that may prevent or treat sars-cov-2 are excluded such as any previous sars-cov-2 vaccine - subjects who have had 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 - 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

- patients who have received second allogeneic hct are not eligible (patients who have undergone a previous autologous hct are eligible - systemic corticosteroids required for chronic conditions at doses > 0.5mg/kg/day prednisone equivalent - patients on maintenance therapies (e.g. rituximab, bruton tyrosine kinase inhibitors, janus kinase inhibitors), who may have significantly attenuated response to vaccination - subjects using investigational or licensed agents that may prevent or treat sars-cov-2 are excluded such as any previous sars-cov-2 vaccine - subjects who have had 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 - 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