Saliva-Based Testing for Monitoring Population Immunity to SARS-CoV-2

Robust methods for the large-scale tracking of antibody responses following SARS-CoV-2 infection or vaccination against the virus are critical for accurate surveillance and assessment of population immunity. Researchers from the USA assessed the durability of IgG antibodies against three SARS-CoV-2 antigens in saliva samples collected from more than 200 people upto 8 months after they were positive for the virus.

The study is published on a pre-print server. The researchers developed and validated a multiplex bead-based immunoassay for the detection of antibody responses against three SARS-CoV-2 antigens in saliva. This assay was used to assess 531 saliva samplestaken from 341 individuals upto 8 months after they tested PCR-positive for SARS-CoV-2.

The team found that the antigen-specific antibody levels peaked at around 30 days post symptom onset, after which decay of the IgGs was assessed in 268 saliva samples taken from 237 people. The estimated IgG half-life was 64 days for the nucleocapsid protein, 100 days for the RBD, and 148 days for the spike protein.

The researchers say these half-life estimates for the salivary IgGs are comparable to those previously reported for plasma IgGs: 67 days for the nucleocapsid protein, 83 days for the RBD, and 140 days for the spike. The majority of saliva samples from individuals who developed COVID-19 were positive for IgGs specific to the nucleocapsid protein (92%), the RBD (95%), and the spike (93%) between 1 and 6 months after symptom onset. The proportion of saliva samples that tested positive for these IgGs between 6 and 8 months after symptom onset was 32% for the nucleocapsid protein, 68% for the RBD, and 59% for the spike. Overall these results support the utility of saliva as an accurate and non-invasive alternative for longitudinal SARS-CoV-2 antibody testing and large-scale surveillance.

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