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.