Strengths and Limitations
Our study presents some significant advantages. First, the study
population was unique in that it enabled us to analyze only patients
infected with the Omicron variant and without any previous SARS-CoV-2
exposure. Second, our study cohort of pregnant women differed from those
of previous studies with an extremely high rate (95.5%) of vaccine
coverage. (7) All of the included 85 pregnant women had received one or
more vaccinations. Third, a clear temporal relationship was established
between maternal and cord serum antibodies. Both the timing of maternal
SARS-CoV-2 infection and maternal SARS-CoV-2 vaccination were well
documented in all our included cases. Fourth, a similar rising trend in
the TR was observed in both the anti-S and anti-N from vaccinated or
infected maternal-fetal pairs, suggesting that the previously proposed
lower TRs in the third trimester or in infected individuals may be
influenced by time. Lastly, our results showed that mothers and newborns
would receive the greatest protection at birth if the mother received
her last vaccination during the third trimester, as indicated by
maternal and cord serum anti-S antibody levels and neutralizing
antibodies.
However, our study has some limitations. The sample size was relatively
small, and data on serial follow-up of antibody titers were not
available; therefore, we could not address the dynamic changes in
antibody titers in individuals. Additionally, maternal-acquired passive
immunity includes not only immunoglobulin but also cellular responses,
such as the vertical transfer of pathogen-specific T cells.(9) Our focus
was solely on the measurable immunoglobulin titer from maternal and cord
serum. Further research that specifically examines cellular level and on
functional activity may provide additional insights into the neonatal
immunity.