Evaluation and deployment of isotype-specific salivary antibody assays for detecting previous SARS-CoV-2 infection in children and adults
Amy Thomas, Elizabeth Oliver, Holly E. Baum, Kapil Gupta, Kathryn L. Shelley, Anna E. Long, Hayley E. Jones, Joyce Smith, Benjamin Hitchings, Natalie Di Bartolo, Kate Vasileiou, Fruzsina Rabi, Hanin Alamir, Malak Eghleilib, Ore Francis, Jennifer Oliver, Begonia Morales‐Aza, Ulrike Obst, Debbie Shattock, Rachael Barr, Lucy Collingwood, Kaltun Duale, Niall Grace, Guillaume Gonnage Livera, Lindsay Bishop, Harriet Downing, Fernanda Rodrigues, Nicholas J. Timpson, Caroline L. Relton, Ashley M. Toye, Derek N. Woolfson, Imre Berger, Anu Goenka, Andrew D. Davidson, Kathleen M. Gillespie, Alistair J.K. Williams, Mick Bailey, Ellen Brooks‐Pollock, Adam Finn, Alice Halliday, the CoMMinS Study Team, Hanin Alamir, Holly E. Baum, Anu Goenka, Alice Halliday, Ben Hitchings, Elizabeth Oliver, Debbie Shattock, Joyce Smith, Amy C. Thomas, David Adegbite, Rupert Antico, Jamie Atkins, Edward Baxter, Lindsay Bishop, Adam Boon, Emma Bridgeman, Lucy Collingwood, Catherine Derrick, Leah Fleming, Ricardo Garcı́a, Guillaume Gonnage Liveria, Niall Grace, Lucy Grimwood, Jane Kinney, Rafaella Myrtou, Alice O’Rouke, Jenny Oliver, Chloe Payne, Rhian Pennie, Millie Powell, Laura García, Aoife Storer-Martin, John Summerhill, Amy L. Taylor, Zoe Taylor, Helen Thompson, Samantha Thomson-Hill, Louis E. Underwood, Gabriella Valentine, Stefania Vergnano, Amelia Way, Maddie White, A. R. Williams, David T. Allen, Josh Anderson, Mariella Ardeshir, Michael Booth, Charles E. Butler, Monika Chaulagain, Alex Darling, Nicholas Dayrell-Armes, Kaltun Duale, Malak Eghleilib, Chloe Farren, Danny Freestone, Jason Harkness, William Healy, Milo Jeenes Flanagan, Maria Khalique
Abstract
BACKGROUND: Saliva is easily obtainable non-invasively and potentially suitable for detecting both current and previous SARS-CoV-2 infection, but there is limited evidence on the utility of salivary antibody testing for community surveillance. METHODS: We established 6 ELISAs detecting IgA and IgG antibodies to whole SARS-CoV-2 spike protein, to its receptor binding domain region and to nucleocapsid protein in saliva. We evaluated diagnostic performance, and using paired saliva and serum samples, correlated mucosal and systemic antibody responses. The best-performing assays were field-tested in 20 household outbreaks. RESULTS: We demonstrate in test accuracy (N = 320), spike IgG (ROC AUC: 95.0%, 92.8-97.3%) and spike IgA (ROC AUC: 89.9%, 86.5-93.2%) assays to discriminate best between pre-pandemic and post COVID-19 saliva samples. Specificity was 100% in younger age groups (0-19 years) for spike IgA and IgG. However, sensitivity was low for the best-performing assay (spike IgG: 50.6%, 39.8-61.4%). Using machine learning, diagnostic performance was improved when a combination of tests was used. As expected, salivary IgA was poorly correlated with serum, indicating an oral mucosal response whereas salivary IgG responses were predictive of those in serum. When deployed to household outbreaks, antibody responses were heterogeneous but remained a reliable indicator of recent infection. Intriguingly, unvaccinated children without confirmed infection showed evidence of exposure almost exclusively through specific IgA responses. CONCLUSIONS: Through robust standardisation, evaluation and field-testing, this work provides a platform for further studies investigating SARS-CoV-2 transmission and mucosal immunity with the potential for expanding salivo-surveillance to other respiratory infections in hard-to-reach settings.