Participants.
VIRUS
Healthy nonpregnant adults aged 18 to 60 years were eligible for inclusion (see supplemental materials for full eligibility criteria). Participants were negative for spike (S) protein antibodies at screening and had no known history of prior exposure to SARS-CoV-2 virus or vaccination. The study was done at Mount Sinai Hospital (New York City, New York, USA) following approval by Advarra IRB (no. Pro00046735). All participants gave written informed consent before enrollment. The study is registered with 