Evaluating the SARS-CoV-2 Specific Antibodies in Saliva

Molecular assays on nasopharyngeal swabs act as the confirmatory test in CoronaVIrus Disease (COVID-19) diagnosis. Despite massive efforts had been made, the high technicalities of nasopharyngeal sampling and molecular assays limit the testing capabilities. Currently, the use of saliva for diagnosis has been recently suggested for COVID-19 diagnostic testing. In a recent research, salivary IgA was associated with the presence of pneumonia, which might illuminate that salivary IgA was independent from serum immunoglobulins. In this study, a total of 44 patients diagnosed with COVID-19 in the Third People’s Hospital of Shenzhen were enrolled. Saliva specimens and serum specimens were obtained at different time points and the immunoglobulins against the SARS-CoV-2 was measured. The results showed that saliva IgA presented higher COI value than IgG and IgM. In matched saliva and serum samples, all saliva presented lower IgG level than serum, and only one saliva sample presented higher IgM level. The conversion rates of saliva IgA and the detection of viral nucleic acid were analyzed in the first and second week after hospitalization. The positive rates were obviously increased when combining the saliva IgA and viral nucleic acid detection. Saliva IgA could serve as useful index for early diagnosis of COVID-19.