key inclusion criteria: 1. meets ≥1 of the following criteria: * is immunocompromised, including people with transplant, who have cancer, primary immunodeficiencies, hiv, rheumatological disease, autoimmune disease, multiple sclerosis or * currently taking immunosuppressant drugs 2. have been fully vaccinated against covid-19 or deemed medically ineligible to receive full course of vaccine 3. has documented negative serology/antibody response in an anti-sars-cov-2 spike protein igg clinical test or ≤50 u/ml on the elecsys® sars-cov-2 s total ig test 4. tested negative for the covid-19 virus within 72 hours prior to randomization key

key inclusion criteria: 1. meets ≥1 of the following criteria: * is immunocompromised, including people with transplant, who have cancer, primary immunodeficiencies, hiv, rheumatological disease, autoimmune disease, multiple sclerosis or * currently taking immunosuppressant drugs 2. have been fully vaccinated against covid-19 or deemed medically ineligible to receive full course of vaccine 3. has documented negative serology/antibody response in an anti-sars-cov-2 spike protein igg clinical test or ≤50 u/ml on the elecsys® sars-cov-2 s total ig test 4. tested negative for the covid-19 virus within 72 hours prior to randomization key

key inclusion criteria: meets ≥1 of the following criteria: is immunocompromised, including people with transplant, who have cancer, primary immunodeficiencies, hiv, rheumatological disease, autoimmune disease, multiple sclerosis or currently taking immunosuppressant drugs have been fully vaccinated against covid-19 or deemed medically ineligible to receive full course of vaccine has documented negative serology/antibody response in an anti-sars-cov-2 spike protein igg clinical test or ≤50 u/ml on the elecsys® sars-cov-2 s total ig test tested negative for the covid-19 virus within 72 hours prior to randomization key

key inclusion criteria: meets ≥1 of the following criteria: is immunocompromised, including people with transplant, who have cancer, primary immunodeficiencies, hiv, rheumatological disease, autoimmune disease, multiple sclerosis or currently taking immunosuppressant drugs have been fully vaccinated against covid-19 or deemed medically ineligible to receive full course of vaccine has documented negative serology/antibody response in an anti-sars-cov-2 spike protein igg clinical test or ≤50 u/ml on the elecsys® sars-cov-2 s total ig test tested negative for the covid-19 virus within 72 hours prior to randomization key

key inclusion criteria: meets ≥1 of the following criteria: is immunocompromised, including people with transplant, who have cancer, primary immunodeficiencies, hiv, rheumatological disease, autoimmune disease, multiple sclerosis or currently taking immunosuppressant drugs have been fully vaccinated against covid-19 or deemed medically ineligible to receive full course of vaccine has documented negative serology/antibody response in an anti-sars-cov-2 spike protein igg clinical test collected ≤72 hours prior to randomization tested negative for the covid-19 virus key

key inclusion criteria: meets ≥1 of the following criteria: is immunocompromised, including people with transplant, who have cancer, primary immunodeficiencies, hiv, rheumatological disease, autoimmune disease, multiple sclerosis or currently taking immunosuppressant drugs have been fully vaccinated against covid-19 or deemed medically ineligible to receive full course of vaccine has documented negative serology/antibody response in an anti-sars-cov-2 spike protein igg clinical test collected ≤72 hours prior to randomization tested negative for the covid-19 virus key

key inclusion criteria: 1. meets ≥1 of the following criteria: - is immunocompromised, including people with transplant, who have cancer, primary immunodeficiencies, hiv, rheumatological disease, autoimmune disease, multiple sclerosis or - currently taking immunosuppressant drugs 2. have been fully vaccinated against covid-19 or deemed medically ineligible to receive full course of vaccine 3. has documented negative serology/antibody response in an anti-sars-cov-2 spike protein igg clinical test collected ≤72 hours prior to randomization 4. tested negative for the covid-19 virus key

key inclusion criteria: 1. meets ≥1 of the following criteria: - is immunocompromised, including people with transplant, who have cancer, primary immunodeficiencies, hiv, rheumatological disease, autoimmune disease, multiple sclerosis or - currently taking immunosuppressant drugs 2. have been fully vaccinated against covid-19 or deemed medically ineligible to receive full course of vaccine 3. has documented negative serology/antibody response in an anti-sars-cov-2 spike protein igg clinical test collected ≤72 hours prior to randomization 4. tested negative for the covid-19 virus key