We used a noninvasive electrochemical quantitative assay for IgG Abs to SARS-CoV-2 S1 Ag in saliva to investigate the kinetics of Ab response in a community-based population that had received either the Pfizer or Moderna mRNA-based vaccine. Samples were received from a total of 97 individuals, including a subset of 42 individuals who collected samples twice weekly for 3 mo or longer. In all, >840 samples were collected and analyzed. In all individuals, salivary SARS-CoV-2 S1 IgG Ab levels rose sharply in the 2-wk period after their second vaccination, with peak Ab levels seen at 10-20 d after vaccination. We observed that 20%, 10%, and 2.4% of individuals providing serial samples had a 90%, 95%, and 99% drop, respectively, from peak levels during the duration of monitoring, and in two patients, Abs fell to prevaccination levels (5%). The use of noninvasive quantitative salivary Ab measurement can allow widespread, cost-effective monitoring of vaccine response.
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