RNA extraction and quantitative reverse transcription PCR analysis
Quantitative reverse transcription polymerase chain reaction (qRT −PCR) was used for SARS-CoV-2 viral load quantification. The nucleic acids in the saliva samples were extracted (QIASymphony DSP Virus/Pathogen kit; Qiagen, Hilden, Germany), and the RNA amount and integrity in all the samples were checked (Nanodrop™; Thermo Fisher Scientific, Waltham, MA, USA). cDNA was generated based on the manufacturer’s instructions (XGEN Master COVID-19) and as described in our previous studies (