Conclusion
Our findings showed that the level of antibody peaked at two months after either vaccination or infection, and a booster-like effect was observed following a recent SARS-CoV-2 infection. Our results suggest that a booster dose of the vaccine during the third trimester can provide maximum transplacental protection against both the Wuhan wild-type strain and Omicron variant. Based on these results, we encourage pregnant women to receive vaccination during pregnancy with a focus on the third trimester for optimal protection.