To determine whether protective antibody levels increase after booster dosing with the Moderna COVID-19 vaccine in patients diagnosed with Hematologic Malignancies who have low antibody levels after a prior first vaccination with any of the SARS-CoV2 vaccines that were authorized for use in the USA. Researchers will also assess whether the booster dosing with the Moderna COVID-19 vaccine is safe in patients with multiple myeloma, amyloidosis, or other blood cancers.

The specific hypothesis being tested is that it may be possible to induce a protective humoral immune response with a booster dose of the Moderna COVID-19 vaccine in patients with hematologic malignancies who did not have an adequate response to first vaccination with any of the available COVID-19 vaccines. To test this hypothesis, t a Phase II singlestage trial in which patients with a negative or weak positive anti-SARS-CoV2 IgG antibody test (defined as <1.00 S/CO and 1.00-1.99 S/CO, respectively) will receive a single standard dose of the Moderna COVID-19 vaccine intramuscularly, and then have anti-SARS-CoV2 IgG antibody levels checked 28 days (+/-3 days) later.

Inclusion Criteria:

1. Provision of signed and dated informed consent form
2. Stated willingness to comply with all study procedures and availability for the duration of the study
3. Male or female, aged 18 years of age or older
4. Previously diagnosed with MM/AL amyloidosis (Cohorts 1 or 3) or other hematologic malignancy (Cohorts 2 or 3).
5. Previously received any one of the available COVID-19 vaccines (between 4 and 36 weeks prior to enrollment)
6. Anti-SARS-CoV2 IgG antibody titer of results less than 1.0 units (Cohorts 1 and 2), or 1.0-1.99 units (Cohort 3). Antibody titers will be measured within 14 days of enrollment.
7. If currently receiving potentially immunosuppressive anti-neoplastic therapy for their underlying hematologic condition, a two-week interruption in therapy before and after the booster dose of vaccine is ENCOURAGED BUT NOT REQUIRED (physician discretion).-

Exclusion Criteria:

1. Daily corticosteroids at a dose equivalent to Prednisone 20 mg/day or greater during the period two weeks before enrollment to the trial. Intermittent steroid dosing at or above this level is permitted (i.e., weekly dexamethasone dosing as part of myeloma therapy)
2. History of previous severe reaction to any available COVID-19 vaccine (defined as any Grade 3 or higher reaction)
3. Febrile illness within 3 days of booster dosing.
4. Documented SARS-CoV2 infection within 2 weeks of enrollment.
5. Less than 3 months post-autologous or allogeneic stem cell transplant (NOTE: transplant between initial standard vaccine administration and enrollment is NOT otherwise grounds for exclusion from participation).

Daily phone calls or video chats for 1 week following vaccine administration, and then weekly after that until 4 weeks after vaccination.