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

Background. Declining humoral immunity in coronavirus disease 2019 (COVID-19) patients and possible 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
prepandemic (n = 35, cohort 3).
Results. Salivary IgG antibody responses in cohort 1 (mainly mild COVID-19) were detectable up to 9 months postrecovery,
with high correlations between spike and nucleocapsid specificity. At 9 months, IgG remained in blood and saliva in most patients.
Salivary IgA was rarely detected at this time point. In cohort 2, salivary IgG and IgA responses were significantly associated with recent
history of COVID-19–like symptoms. Salivary IgG tolerated temperature and detergent pretreatments.
Conclusions. Unlike SARS-CoV-2 salivary IgA that appeared short lived, specific saliva IgG appeared stable even after mild
COVID-19, as for blood serology. This noninvasive saliva-based SARS-CoV-2 antibody test with home self-collection may be a complementary
alternative to conventional blood serology.