Research Highlights: COVID-19 mRNA Vaccines Activate Immune System in Pregnant and Lactating Women

close up photo of pregnant woman in white dress holding her stomach
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COVID-19 mRNA Vaccines Activate Immune System in Pregnant and Lactating Women

  • Studies have shown that COVID-19 increases the risk for morbidity and mortality in pregnant women however, these women have not been included in phase 3 COVID-19 vaccine trials.
  • As a result, information regarding the immunogenicity and vaccine safety in these group are lacking.
  • Researchers evaluated the immunogenicity of COVID-19 messenger RNA vaccines in pregnant and lactating women.
  • The study includes an evaluation of the mRNA vaccines against emerging SARS-CoV-2 variants.
  • The team is led by Dr. Ai-ris Y. Collier of Beth Israel Deaconess Medical Center in Boston, Massachusetts.
  • Enrollees include 103 women, aged 18 to 45 years, who received the COVID-19 vaccine from December 2020 to March 2021 and 28 women who had confirmed COVID-19 from April 2020 to March 2021.
  • The study includes 30 pregnant, 16 lactating, and 57 neither pregnant nor lactating who received either the Moderna vaccine (mRNA-1273) or Pfizer-BioNTech vaccine (BNT162b2) and 22 pregnant and 6 non-pregnant unvaccinated women with COVID-19 viral infection.
  • Immune responses from pregnant, lactating, and non-pregnant women were assessed after vaccination.
  • After the second vaccine dose, 4 pregnant, 7 lactating, and 27 non-pregnant women reported fever.
  • Antibody responses and T cell responses were detected in pregnant, lactating, and non-pregnant women after vaccination.
  • Researchers also observed that the infant cord blood and breast milk have binding and neutralizing antibodies.
  • The concentrations of binding and neutralizing antibodies against B.1.1.7 and B.1.351 variants were reduced.
  • However, T cell responses were preserved against viral variants.
  • In conclusion, the COVID-19 mRNA vaccines activated the immune system in pregnant women and vaccine-induced antibodies were transferred to infant cord blood and breast milk
  • Vaccinated pregnant and non-pregnant developed cross-reactive antibody and T cell responses against SARS-CoV-2 variants.


Collier AY, McMahan K, Yu J, et al. Immunogenicity of COVID-19 mRNA Vaccines in Pregnant and Lactating Women. JAMA. Published online May 13, 2021. doi:10.1001/jama.2021.7563