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.

Background The world has been confronted with the COVID-19 pandemic for more than one year. Severe disease is more often found among elderly people, whereas most young children and adolescents show mild symptoms or even remain asymptomatic, so that infection might be undiagnosed. Therefore, only limited epidemiological data on SARS-CoV-2 infection in children and young adults are available. Objective This study aims to determine the prevalence of SARS-CoV-2 antibodies in children from the city of Tübingen, Germany, and to measure the incidence of new cases over 12 months. Methods SARS-CoV-2 antibodies will be measured in saliva as a surrogate for a previous SARS-CoV-2 infection. Children will be sampled at their preschools, primary schools, and secondary schools at three time points: July 2020, October to December 2020, and April to July 2021. An adult cohort will be sampled at the same time points (ie, adult comparator group). The saliva-based SARS-CoV-2–antibody enzyme-linked immunosorbent assay will be validated using blood and saliva samples from adults with confirmed previous SARS-CoV-2 infections (ie, adult validation group). Results The first study participant was enrolled in July 2020, and recruitment and enrollment continued until July 2021. We have recruited and enrolled 1850 children, 560 adults for the comparator group, and 83 adults for the validation group. We have collected samples from the children and the adults for the comparator group at the three time points. We followed up with participants in the adult validation group every 2 months and, as of the writing of this paper, we were at time point 7. We will conduct data analysis after the data collection period. Conclusions Infection rates in children are commonly underreported due to a lack of polymerase chain reaction testing. This study will report on the prevalence of SARS-CoV-2 infections in infants, school children, and adolescents as well as the incidence change over 12 months in the city of Tübingen, Germany. The saliva sampling approach for SARS-CoV-2–antibody measurement allows for a unique, representative, population-based sample collection process. Trial Registration ClinicalTrials.gov NCT04581889; https://clinicaltrials.gov/ct2/show/NCT04581889 International Registered Report Identifier (IRRID) DERR1-10.2196/27739

BACKGROUND The world is confronted with the Coronavirus Disease-2019 (COVID-19) pandemic caused by the SARS-CoV-2 virus responsible for a continuously rising number of cases and deaths. Severe disease is more often found in elderly people, whereas young children and adolescents rather only show mild symptoms or even remain asymptomatic, so that infection might be undiagnosed. Therefore, only limited epidemiological data on SARS-CoV-2 infection in children and young adults are available. OBJECTIVE This study aims to determine the prevalence of SARS-CoV-2 antibodies in children in a defined area, the city of Tübingen, Germany, and to follow the incidence of new cases in 12 months of follow-up. METHODS SARS-CoV-2 reactive antibodies will be measured in saliva as a surrogate for a previous SARS-CoV-2 infection. Collection procedures are non-invasive and are thus amenable for epidemiologic studies that require representative population-based sampling. Children will be sampled via day care institutions and schools at three time points: starting in German summer 2020, before winter and after winter. An adult cohort will be sampled at the same time points for comparison (adult comparator group). The saliva sampling approach for SARS-CoV-2 antibody measurement allows a unique and representative, population-based sample collection. The saliva-based SARS-CoV-2 antibody ELISA is validated with blood and saliva sampled from adults with confirmed previous SARS-CoV-2 infection (adult validation group). RESULTS Recruitment of participants to this study began in July 2020, and data collection will continue for a planned study period of 12 months. CONCLUSIONS Infection rates in children are commonly underreported due to lack of PCR testing. The study will inform about the prevalence of SARS-CoV-2 infections in children and the incidence change over the upcoming 12 months (2020/2021) in a defined area, the city of Tübingen, Germany. Prevalence data in different age cohorts such as infants, school children, adolescents will be evaluated. The saliva sampling approach for SARS-CoV-2 antibody measurement allows a unique and representative, population-based sample collection. Tübingen is a middle-sized University City in the South of Germany, and prevalence maybe informative for similar areas. CLINICALTRIAL Retrospectively registered at ClinicalTrials.gov: NCT04581889, 10 October, 2020. Acronym: Coro-buddy.