Non-Invasive Antibody Assessment in Saliva to Determine SARS-CoV-2 Exposure in Young Children

Abstract

Saliva is a body fluid with hitherto unused potential for the assessment of SARS-CoV-2 antibodies. Specific antibodies can indicate a past SARS-CoV-2 infection and allow to estimate the proportion of individuals with a potential protective immunity. First, we carefully characterized plasma samples obtained from adult control groups with and without prior SARS-CoV-2 infection using certified reference ELISAs. Simultaneously collected saliva samples of confirmed convalescent and negative individuals where then used to validate the herein newly developed ELISA for the detection of SARS-CoV-2 IgG antibodies in saliva. The saliva ELISA was applied to assess SARS-CoV-2 exposure in young children (N = 837) in the age between 1 and 10 years in Tübingen, Germany, towards the end of the first pandemic year 2020. Sensitivity and specificity of the new saliva ELISA was 87% and 100%, respectively. With 12% of all Tübingen children sampled via their respective educational institutions, estimates of SARS-CoV-2 antibody prevalence was 1.6%. Interestingly, only 0.4% preschool kids were positive compared to 3.0% of primary school children. Less than 20% of positive children self-reported symptoms within two months prior to saliva sampling that could be associated - but not exclusively - with a SARS-CoV-2 infection. The saliva ELISA is a valid and suitable protocol to enable population-based surveys for SARS-CoV-2 antibodies. Using non-invasive sampling and saliva ELISA testing, we found that prevalence of SARS-CoV-2 antibodies was significantly lower in young children than in primary school children.

SARS-CoV-2 Antibodies Are Persisting in Saliva for More Than 15 Months After Infection and Become Strongly Boosted After Vaccination

“…Sample processing and storage was done as published recently ( 12 ). Briefly, saliva was collected by spitting into a sterile container (3ml) (Multi-purpose containers 30ml Greiner Bio-One ref.…”

“…IgG reactive to SARS-CoV-2 RBD were measured by a meticulously established and validated in-house ELISA ( 12 , 13 ) for IgG detection in saliva as well as by an in-house ELISA specifically established to analyze plasma antibodies (see Supplementary Material ). Briefly, the SARS-CoV-2 RBD antigen was diluted in 1x PBS to a final concentration of 2 μg/ml and added per well to high binding plates.…”

“…The plate was read at 450 nm and 620 nm with a microplate reader (CLARIOstar, BMG LABTECH). Cut-off for salivary SARS-CoV-2 IgG positivity was previously set to 6.3 ng/ml ( 12 ).…”

“…The detection antibody was diluted 1:5,000 in 1x ROTI Block buffer and incubated for 30 min (RT, 700 rpm). The IgG concentration is presented in µg/ml.and the cut-of value was set to 4.0 µg/ml ( 12 ). For confirmation, plasma samples were re-analyzed by the commercial, CE certified SARS-CoV-2 IgG ELISA (EUROIMMUN) detecting antibodies binding to SARS-CoV-2 Spike protein domain S1 and the assays were performed following the manufacturer’s instructions.…”

Prevalence of SARS-CoV-2 Infection in Children by Antibody Detection in Saliva: Protocol for a Prospective Longitudinal Study (Coro-Buddy)

“…Saliva and blood samples were processed according to standard procedures and stored at –20 °C until analysis by ELISA to identify SARS-CoV-2–reactive antibodies. A previously established and validated in-house ELISA to detect antibodies against SARS-CoV-2 in saliva was performed [ 20 ]. Blood samples from the validation group cohort will be analyzed using a certified commercial ELISA by EUROIMMUN to quantify immunoglobulin G reactive to the S1 domain of the of SARS-CoV-2 spike protein.…”