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.