COVID-19 Serology at population scale: SARS-CoV-2-specific antibody responses in saliva

Pisanic et al., (2020) J Clin Microbiol.

ABSTRACT: SARS-CoV-2 is the cause of an ongoing pandemic that has infected over 36 million and killed over 1 million people. Informed implementation of government public health policies depends on accurate data on SARS-CoV-2 immunity at population scale. We hypothesized that detection of SARS-CoV-2 salivary antibodies could serve as a non-invasive alternative to serological testing for monitoring of SARS-CoV-2 infection and seropositivity at population scale. We developed a multiplex SARS-CoV-2 antibody immunoassay based on Luminex technology that comprised 12 CoV antigens, mostly derived from SARS-CoV-2 nucleocapsid (N) and spike (S). Saliva and sera collected from confirmed COVID-19 cases and from the pre-COVID-19 era were tested for IgG, IgA and IgM to the antigen panel. Matched saliva and serum IgG responses (n=28) were significantly correlated. The salivary anti-N IgG response resulted in highest sensitivity (100%), exhibiting a positive response in 24/24 RT-PCR-confirmed COVID-19 cases sampled at >14 days post-symptom onset (DPSO), whereas the salivary anti-receptor binding domain (RBD) IgG response yielded 100% specificity. Temporal kinetics of IgG in saliva were consistent with those observed in blood and indicated that most individuals seroconvert around 10 DPSO. Algorithms employing a combination of the IgG response to N and S antigens result in high diagnostic accuracy (100%) as early as 10 DPSO. These results support the use of saliva-based antibody testing as a non-invasive and scalable alternative to blood-based antibody testing.

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Keywords: SARS-CoV-2, COVID-19, antibodies, immunity, serological testing, IgA, IgG, IgM