Salivary IgG antibody response to SARS-CoV-2 as a non-invasive assessment of immune response. Differences between vaccinated children and adults

Background Studies comparing systemic and salivary antibody responses against SARS-CoV-2 between children and adults show conflicting results. Furthermore, it is still unclear whether salivary antibody testing could be a non-invasive approach to evaluate the humoral immune response.

anti-SARS-CoV-2 IgG antibodies were measured in blood and saliva sample pairs from vaccinated adults to investigate whether salivary antibody response could be a non-invasive assessment of immune response. Salivary antibody levels were also compared between vaccinated children and adults to investigate local antibody responses.

Salivary IgG antibody response against SARS-CoV-2 largely reflects the systemic response in vaccinated adults. Salivary and systemic antibody concentrations were higher in vaccinated adults who had been infected, received schedules including mRNA-based vaccines, had more exposures, and a shorter time from last exposure. Salivary antibody detection was associated with schedules including mRNA-based vaccines, time from last exposure, and systemic antibody concentrations. Vaccinated children showed higher salivary antibody concentrations than adults. This difference remained when comparing antibody levels between children and adults under equal conditions (vaccination schedules, number of exposures, time from last exposure, COVID-19 history). Younger age, number of exposures, schedules including mRNA-based vaccines, and shorter time from last exposure were associated with salivary antibody levels in a multivariable linear regression analysis (p< 0.0001).

Salivary antibody determination against SARS-CoV-2 could be a non-invasive assessment of the short-term immune response in adults with multiple exposures. Furthermore, the stronger salivary antibody response in children suggests that local immune protection may differ between children and adults, contributing to different outcomes. Competing Interest Statement The authors have declared no competing interest. Funding Statement This study was supported by a grant from CONICET (PIP 11220210100378CO). Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: This study was approved by the local Ethics Committee of the Academia Nacional de Medicina I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable. Yes Footnotes Data availability statement: The data that support the findings of this study are available from the corresponding author upon reasonable request. Funding/Support: This study was supported by a grant from CONICET (PIP 11220210100378CO). Conflict of Interest Disclosure: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Ethics Statement: This study was approved by the Academia Nacional de Medicina Ethics Committee. Consent Statement: Written informed consent was obtained from adult participants and from parents for children participants. More samples were added, so the data and figures were updated. Data Availability All data produced in the present study are available upon reasonable request to the authors Abbreviations - BAU - binding antibody units - BAU/mL - per mL - GMC - geometric mean concentrations - 95% CI - 95% confidence intervals.