Due to lack of data on vaccine safety and immunogenicity in Pregnant and Lactating Women Collier A.Y. et al. carried out a study to evaluate the immunogenicity of COVID-19 messenger RNA (mRNA) vaccines in such population, including against emerging SARS-CoV-2 variants of concern.

The study included 30 pregnant, 16 lactating, and 57 neither pregnant nor lactating women who received either the mRNA-1273 (Moderna) or BNT162b2 (Pfizer-BioNTech) COVID-19 vaccines and also 22 pregnant and 6 nonpregnant unvaccinated women with SARS-CoV-2 infection.

The enrolled individuals were subjected to assessment of SARS-CoV-2 receptor binding domain binding, neutralizing, and functional non-neutralizing antibody responses following vaccination. 

They observed-

Presence of- Binding, neutralizing, and functional non-neutralizing antibody responses, as well as CD4 and CD8 T-cell responses in pregnant, lactating, and nonpregnant women following vaccination. 

Presence of- Binding and neutralizing antibodies in infant cord blood and breast milk. 

Reduction in- Binding and neutralizing antibody titers against the SARS-CoV-2 B.1.1.7 and B.1.351 variants of concern, but T-cell responses were preserved against viral variants.

Thus they concluded that receipt of a COVID-19 mRNA vaccine is immunogenic in pregnant women, and vaccine-elicited antibodies are transported to infant cord blood and breast milk. 

All the Vaccinated women developed cross-reactive antibody responses and T-cell responses against SARS-CoV-2 variants of concern.

Source-Collier AY, McMahan K, Yu J, et al. Immunogenicity of COVID-19 mRNA Vaccines in Pregnant and Lactating Women. JAMA. 2021. doi:10.1001/jama.2021.7563