Material and Methods
In our original clinical study, enrolled participants in the mRNA-1273 and BNT162b cohorts provided one self-collected saliva specimen for anti-S-protein IgG testing following their first and second vaccination doses at predetermined time intervals and every thirty days thereafter17. Booster study enrollment was offered to participants who had been enrolled in our previous two-dose regimen study17. Recruitment took place among individuals who were due to receive the third-dose booster vaccine of either the mRNA-1273 or BNT162b2 vaccines, constituting two independent cohorts.
Participants enrolled in the booster study in the mRNA-1273 cohort provided a saliva specimen 46 days after vaccination, on average, and every 30 days thereafter for 7 months. Participants enrolled during their third vaccine dose of the BNT162b2 vaccine provided a specimen a few days before, or on the day of vaccination, as well as on days 5, 11, 16, 20, 30, 60, 90, and every 30 days thereafter. Participants who received a positive Ab test at the first time point, or prior to enrollment, or who missed one collection time point, were excluded from the original clinical study. During the booster study, participants who received a positive PCR test before or after receiving the booster vaccine were excluded from the study.
The anti-SARS-CoV-2 IgG ELISA was performed, as previously described17. The Limit of Detection (LOD) was 1 ng/mL, and the Limit of Quantification (LOQ) was 1.5 ng/mL. All statistical analysis, and plots were generated using GraphPad Prism Software (GraphPad Prism, San Diego, USA). Paired t-tests were used to compare the second and third vaccine dose peak anti-S-protein IgG titers for each cohort.