BACKGROUND AND PURPOSE:

• Prabhu et al. (Obstetrics & Gynecology, 2021) examined the immunologic response to COVID-19 mRNA vaccination in pregnancy, including transplacental transfer of maternal antibodies

METHODS:

• Cohort study
• Participants
  • Pregnant women with cord blood availability following delivery
  • Received one or both doses of an mRNA–based COVID-19 vaccine
  •  Singleton neonate
  • Exclusions: Positive test against nucleocapsid protein (to verify that antibodies derived from vaccination rather than previous SARS-CoV-2 infection)
• Study design
  • Semi-quantitative testing for antibodies was performed on clinical sera
    • Maternal peripheral blood
    • Cord blood
  • Relationship between maternal and cord blood IgG antibody levels and IgG placental transfer (neonatal/maternal) were assessed  

RESULTS:

• 122 pregnant women
  • One vaccine dose: 55 women
  • Two doses: 67 women
• Antibody response at birth
  • IgG antibodies detected: 87 women
  • IgG and IgM antibodies detected: 19 women
  • No antibody response: 16 women, all of whom were <4 weeks after their first vaccine dose
• All women and cord blood samples, except for one, had detectable IgG antibodies ≥4 weeks after the first vaccine
  • Detectable IgG in cord blood at delivery, after first dose: 44%
  • Detectable IgG in cord blood at delivery, after second dose: 99%
• The earliest detection of antibodies
  • In maternal blood: 5 days post first vaccine dose
  • In cord blood: 16 days post first vaccine dose
• Maternal IgG levels were significantly higher, week by week, ≥2 weeks after the first vaccine dose (P = 0.005)

CONCLUSION:

• Women who received an mRNA COVID-19 vaccine during pregnancy mounted an antibody response as early as 5 days after their first dose
• Antibodies were present in cord blood as early as 16 days after the first dose
• The authors state

The increasing levels of maternal IgG over time and the increasing placental IgG transfer ratio over time suggest that timing between vaccination and birth may be an important factor to consider in vaccination strategies of pregnant women

Given the variability in antibody transfer and lack of transfer to one neonate, further studies are needed to understand the factors that influence transplacental transfer of IgG antibodies, as well as the protective nature of these antibodies

Learn More – Primary Sources:

Antibody Response to Coronavirus Disease 2019 (COVID-19) Messenger RNA Vaccination in Pregnant Women and Transplacental Passage Into Cord Blood

Related ObG Topics:

SMFM Guidance on COVID-19 Vaccine in Pregnancy

mRNA COVID-19 Vaccine Safety in Pregnant Women

Vaccines in Pregnant and Lactating Women: Is Immune Response Similar to that of Non-Pregnant Patients?

How Efficient is Transplacental Transfer of SARS-CoV-2 Antibodies?