Purpose

In this Phase 4, open-label trial, participants of the ACTIV-3/TICO clinical trial at selected sites who received certain pre-specified blinded investigational agents or placebo as part of that trial, and who have since achieved sustained recovery, and who are still [TICO assignment] blinded and who are still within 28 to 90 days after initial TICO randomization, will be randomized in this 2x2 factorial design to one of four groups: (i) immediate versus 12 week deferral of first dose administration and also (ii) one dose only, versus two doses to be given 4 weeks apart of the Moderna mRNA-1273 or the Pfizer BNT162b2 vaccine (mRNA vaccines). Choice of Moderna or Pfizer vaccine is determined based on availability at the site. The choice is individual, although participants vaccinated twice should receive the same type of vaccine for both injections. The primary objectives of this 2x2 factorial design are (i) to estimate the difference in neutralizing antibody (NAb) response to the mRNA vaccine from baseline to Week 48 among participants vaccinated early versus deferred, and (ii) to estimate the difference in NAb response to this vaccine among participants vaccinated once versus twice. The primary analyses will be carried out in participants randomized to placebo in TICO. Analyses will also be carried out for those who receive the investigational agent(s) studied in TICO. A key secondary objective is to ascertain the effect, if any, of SARS-CoV-2 monoclonal antibodies, and other interventions that have been studied in hospitalized COVID-19 subjects, on natural and vaccine-induced immunity. Participants will remain blinded to the interventions received in the ACTIV-3/TICO study, however allocation to the timing of vaccination and to one or two vaccinations in this (VATICO) study is not blinded.