Multiplex Antibody Analysis of IgM, IgA and IgG to SARS-CoV-2 in Saliva and Serum from Infected Children and their Close Contacts

Abstract

COVID-19 affects children to a lesser extent than adults but they can still get infected and transmit SARS-CoV-2 to their contacts. Field deployable non-invasive sensitive diagnostic techniques are needed to evaluate the infectivity dynamics of the coronavirus in pediatric populations and guide public health interventions. We evaluated the utility of high-throughput Luminex-based assays applied to saliva samples to quantify IgM, IgA and IgG antibodies against five SARS-CoV-2 spike (S) and nucleocapsid (N) antigens in the context of a contacts and infectivity longitudinal study. We compared the antibody levels obtained in saliva versus serum/plasma samples from a group of children and adults tested weekly by RT-PCR over 35 days and diagnosed as positive (n=58), and a group of children and adults who consistently tested negative over the follow up period (n=61), in the Summer of 2020 in Barcelona, Spain. Antibody levels in saliva samples from individuals with confirmed RT-PCR diagnosis of SARS-CoV-2 infection were significantly higher than in negative individuals and correlated with those measured in sera/plasmas. Higher levels of anti-S IgG were found in asymptomatic individuals that could indicate protection against disease in infected individuals. Higher anti-S IgG and IgM levels in serum/plasma and saliva, respectively, in infected children compared to infected adults could also be related to stronger clinical immunity in them. Among infected children, males had higher levels of saliva IgG to N and RBD than females. Despite overall correlation, individual clustering analysis suggested that responses that may not be detected in blood could be patent in saliva, and vice versa, and therefore that both measurements are complementary. In addition to serum/plasma, measurement of SARS-CoV-2-specific saliva antibodies should be considered as a complementary non-invasive assay to better estimate the percentage of individuals who have experienced coronavirus infection. Saliva antibody detection could allow determining COVID-19 prevalence in pediatric populations, alternative to bleeding or nasal swab, and serological diagnosis following vaccination.

Clinical evaluation of the SD Biosensor SARS-CoV-2 saliva antigen rapid test with symptomatic and asymptomatic, non-hospitalized patients

“…Using saliva RDT, despite lower general sensitivity compared to both saliva RT-PCR and nasopharyngeal RDT, based on RT-PCR Ct/viral load values almost all presumed infectious individuals could be detected, however this result could not be compared to nasopharyngeal swab virus culture in the current study. Saliva is a complex material shown to have comparable or slightly lower viral load to nasopharyngeal sample [ 13 ], it also contains SARS-2 specific antibodies [ 14 ] and different viral kinetics compared to nasopharynx which might explain the lower performance in the tested population. Furthermore, we have evaluated this test on non-hospitalized patients and a study found correlation of more severe disease with higher viral load in saliva [ 15 ].…”

Immunological memory to SARS‐CoV‐2 infection and COVID‐19 vaccines

“…The most dramatic example of this is the human papillomavirus (HPV) vaccine, which provides 99% protective immunity in the vaginal tract, even though the vaccine is a conventional intramuscular immunization and elicits circulating IgG. For SARS‐CoV‐2 previously infected individuals, the titers of circulating IgG correlate with saliva IgG, 56,190,197 and the correlation was sustained over a period of 9 months 56 . Correlation between circulating IgA and saliva IgA in previously infected individuals was also substantial over a 9‐month period 56 .…”

Clinical evaluation of the SD Biosensor saliva antigen rapid test with symptomatic and asymptomatic, non-hospitalized patients

“…Using saliva RDT, despite lower general sensitivity compared to both saliva RT PCR and nasopharyngeal RDT, most infectious individuals could be detected, however this result was not compared to nasopharyngeal virus culture. Saliva is a complex material shown to have comparable or slightly lower viral load to nasopharyngeal sampling sites (8), it also contains SARS-2 specific antibodies (9) and different viral kinetics compared to nasopharynx which might explain the lower performance in the tested population. We have evaluated this test on non-hospitalized patients; a study found correlation of more severe disease with higher viral load in saliva (10).…”