* currently hospitalized or judged by the investigator as likely to require hospitalization in the next 24 hours * symptoms consistent with severe covid-19 * participants who, in the judgement of the investigator are likely to die in the next 7 days. * severely immunocompromised participants * for parts a and b, prior receipt of a sars-cov-2 vaccine at any time prior to enrollment (vaccination with an authorized or approved sars-cov-2 vaccine will not be allowed for 90 days after dosing) * for parts b and c, conditions that would prohibit receipt of im injections in the investigator's opinion * for parts a, b and c, receipt of any vaccine within 48 hours prior to enrollment (vaccination with an authorized or approved sars-cov-2 vaccine will not be allowed for 90 days after dosing)

* currently hospitalized or judged by the investigator as likely to require hospitalization in the next 24 hours * symptoms consistent with severe covid-19 * participants who, in the judgement of the investigator are likely to die in the next 7 days. * severely immunocompromised participants * for parts a and b, prior receipt of a sars-cov-2 vaccine at any time prior to enrollment (vaccination with an authorized or approved sars-cov-2 vaccine will not be allowed for 90 days after dosing) * for parts b and c, conditions that would prohibit receipt of im injections in the investigator's opinion * for parts a, b and c, receipt of any vaccine within 48 hours prior to enrollment (vaccination with an authorized or approved sars-cov-2 vaccine will not be allowed for 90 days after dosing)

- currently hospitalized or judged by the investigator as likely to require hospitalization in the next 24 hours - symptoms consistent with severe covid-19 - participants who, in the judgement of the investigator are likely to die in the next 7 days. - severely immunocompromised participants - for parts a and b, prior receipt of a sars-cov-2 vaccine at any time prior to enrollment (vaccination with an authorized or approved sars-cov-2 vaccine will not be allowed for 90 days after dosing) - for parts b and c, conditions that would prohibit receipt of im injections in the investigator's opinion - for parts a, b and c, receipt of any vaccine within 48 hours prior to enrollment (vaccination with an authorized or approved sars-cov-2 vaccine will not be allowed for 90 days after dosing)

- currently hospitalized or judged by the investigator as likely to require hospitalization in the next 24 hours - symptoms consistent with severe covid-19 - participants who, in the judgement of the investigator are likely to die in the next 7 days. - severely immunocompromised participants - for parts a and b, prior receipt of a sars-cov-2 vaccine at any time prior to enrollment (vaccination with an authorized or approved sars-cov-2 vaccine will not be allowed for 90 days after dosing) - for parts b and c, conditions that would prohibit receipt of im injections in the investigator's opinion - for parts a, b and c, receipt of any vaccine within 48 hours prior to enrollment (vaccination with an authorized or approved sars-cov-2 vaccine will not be allowed for 90 days after dosing)

- currently hospitalized or judged by the investigator as likely to require hospitalization in the next 24 hours - symptoms consistent with severe covid-19 - participants who, in the judgement of the investigator are likely to die in the next 7 days. - severely immunocompromised participants

- currently hospitalized or judged by the investigator as likely to require hospitalization in the next 24 hours - symptoms consistent with severe covid-19 - participants who, in the judgement of the investigator are likely to die in the next 7 days. - severely immunocompromised participants