Limitations
Collection of matched serum and saliva specimens from each participant
for the entire duration of the combined mRNA vaccine studies would have
provided more persuasive evidence supporting the correlation of serum
and saliva anti-S-protein IgG titers over time. However, this was not
practical, and would have decreased participation. Nevertheless, we
previously demonstrated our ELISA assay using saliva specimens had
comparable sensitivity and specificity to serum-based
assays15.
Also, the continuous evolution of the S-protein in omicron and other new
variants could have reduced the sensitivity of the ELISA assay to detect
heterogeneous anti-S-protein IgG increases from natural infections.