inclusion criteria: - for all participants: ability and willingness of participant (or legally authorized representative) to provide informed consent prior to initiation of any study procedures. - for all participants: individuals ≥18 years of age - for participants who are in, or who have completed, the activ-2/a5401 trial: receipt of all selected investigational therapy or active comparator/placebo for that therapy at selected sites. - for participants who are in, or who have completed, the activ-2/a5401 trial and will be receiving study-provided moderna mrna-1273 covid-19 vaccine: receipt of the last dose of investigational therapy or active comparator/placebo for that therapy ≥60 days and ≤240 days prior to study entry. - for participants who are in, or who have completed, the activ-2/a5401 trial and will be receiving community-provided mrna-based covid-19 vaccine: receipt of the last dose of investigational therapy or active comparator/placebo for that therapy ≥60 and ≤240 days prior to planned receipt of the first dose of community-provided vaccine.

inclusion criteria: - for all participants: ability and willingness of participant (or legally authorized representative) to provide informed consent prior to initiation of any study procedures. - for all participants: individuals ≥18 years of age - for participants who are in, or who have completed, the activ-2/a5401 trial: receipt of all selected investigational therapy or active comparator/placebo for that therapy at selected sites. - for participants who are in, or who have completed, the activ-2/a5401 trial and will be receiving study-provided moderna mrna-1273 covid-19 vaccine: receipt of the last dose of investigational therapy or active comparator/placebo for that therapy ≥60 days and ≤240 days prior to study entry. - for participants who are in, or who have completed, the activ-2/a5401 trial and will be receiving community-provided mrna-based covid-19 vaccine: receipt of the last dose of investigational therapy or active comparator/placebo for that therapy ≥60 and ≤240 days prior to planned receipt of the first dose of community-provided vaccine.