An Agreement of Antigen Tests on Oral Pharyngeal Swabs or Less Invasive Testing With Reverse Transcription Polymerase Chain Reaction for Detecting SARS-CoV-2 in Adults: Protocol for a Prospective Nationwide Observational Study - Uffe Vest Schneider; Jenny Dahl Knudsen; Anders Koch; Nikolai Søren Kirkby; Jan Gorm Lisby (JMIR Research Protocols, 2022)