Persisting Salivary IgG against SARS-CoV-2 at 9 Months After Mild COVID-19: A Complementary Approach to Population Surveys

Alkharaan, Hassan; Bayati, Shaghayegh; Hellström, Cecilia; Aleman, Soo; Olsson, Annika; Lindahl, Karin; Bogdanovic, Gordana; Healy, Katie; Tsilingaridis, Georgios; De Palma, Patricia; Hober, Sophia; Månberg, Anna; Nilsson, Peter; Pin, Elisa; Sällberg Chen, Margaret

BACKGROUND: Declining humoral immunity in COVID-19 patients and the possibility of reinfection have raised concern. Mucosal immunity, particularly salivary antibodies, may be short-lived although long-term studies are lacking. METHODS: Using a multiplex bead-based array platform, we investigated antibodies specific to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) proteins in 256 saliva samples from convalescent patients 1-9 months after symptomatic COVID-19 (n=74, Cohort 1), undiagnosed individuals with self-reported questionnaires (n=147, Cohort 2), and individuals sampled pre-pandemic time (n= 35, Cohort 3). RESULTS: Salivary IgG antibody responses in Cohort 1 (mainly mild COVID-19) were detectable up to nine months post-recovery, with high correlations between spike and nucleocapsid specificity. At nine months, IgG remained in both blood and saliva in majority of patients. Salivary IgA was rarely detected at this timepoint. In Cohort 2, salivary IgG and IgA responses were significantly associated with a recent history of COVID-19 like symptoms. Salivary IgG also tolerated temperature and detergent pre-treatments. CONCLUSIONS: Unlike SARS-CoV-2 salivary IgA that appeared short-lived, the specific IgG in saliva appeared stable even after mild COVID-19 as noted for blood serology. This non-invasive saliva-based SARS-CoV-2 antibody test with home self-collection may therefore serve as a complementary alternative to conventional blood serology.