Advanced Molecular and Immunological Diagnostic Methods to Detect SARS-CoV-2 Infection

COVID-19 emerged in late 2019 in China and quickly spread across the globe, causing over521 million cases of infection and 6.26 million deaths to date. After 2 years, numerous advances havebeen made. First of all, the preventive vaccine, which has been implemented in record time, is effectivein more than 95% of cases. Additionally, in the diagnostic field, there are numerous molecular andantigenic diagnostic kits that are equipped with high sensitivity and specificity. Real Time-PCR-basedassays for the detection of viral RNA are currently considered the gold-standard method for SARS-CoV-2 diagnosis and can be used efficiently on pooled nasopharyngeal, or oropharyngeal samplesfor widespread screening. Moreover, additional, and more advanced molecular methods such asdroplet-digital PCR (ddPCR), clustered regularly interspaced short palindromic repeats (CRISPR)and next-generation sequencing (NGS), are currently under development to detect the SARS-CoV-2RNA. However, as the number of subjects infected with SARS-CoV-2 continuously increases globally,health care systems are being placed under increased stress. Thus, the clinical laboratory plays animportant role, helping to select especially asymptomatic individuals who are actively carrying the live replicating virus, with fast and non-invasive molecular technologies. Recent diagnostic strategies,other than molecular methods, have been adopted to either detect viral antigens, i.e., antigen-basedimmunoassays, or human anti-SARS-CoV-2 antibodies, i.e., antibody-based immunoassays, in nasalor oropharyngeal swabs, as well as in blood or saliva samples. However, the role of mucosal sIgAs,which are essential in the control of viruses entering the body through mucosal surfaces, remainsto be elucidated, and in particular the role of the immune response in counteracting SARS-CoV-2infection, primarily at the site(s) of virus entry that appears to be promising.