What are the clinical considerations related to COVID-19 vaccination with regard to pregnancy and lactation?

Updated: Sep 24, 2021
  • Author: David J Cennimo, MD, FAAP, FACP, FIDSA, AAHIVS; Chief Editor: John L Brusch, MD, FACP  more...
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According to data from the CDC, pregnant women are at an increased risk for severe illness from coronavirus disease 2019 (COVID-19) and death, compared with nonpregnant individuals. In addition, pregnant women may be at increased risk for other adverse outcomes (eg, preterm delivery). The CDC has issued Interim Clinical Considerations for Use of mRNA COVID-19 Vaccines, which discusses the limited data available regarding administration to pregnant women. Owing to these risks, preventing severe COVID-19 infection is essential for both mother and fetus. 

A cohort study (n = 131) by Gray et al found mRNA SARS-CoV-2 vaccines generated humoral immunity in pregnant and lactating women, similarly to that observed in nonpregnant women. All serum titers from vaccination were significantly higher compared with titers induced by SARS-CoV-2 infection during pregnancy (p < 0.0001). Importantly, vaccine-generated antibodies were present in all umbilical cord blood and breastmilk samples, showing immune transfer to neonates vial placenta and breastmilk. [55] In another study, maternal and cord blood sera were collected from 20 parturients who received 2 doses of the mRNA BNT162b2 vaccine. All women and infants were positive for anti S- and Anti-RBD-specific IgG. [56]   

Additional studies support the above findings in cord blood and provide further information regarding potential timing of maternal vaccination. In one study (n = 27), mean placental IgG transfer ratio following vaccination (mRNA vaccines) provides about an equal in infant antibody level to maternal level. It also appears to increase with latency from vaccination, suggesting that earlier vaccination in the third trimester may produce greater infant immunity. [57]   A similar study (n = 122) observed women vaccinated with mRNA vaccines lead to maternal antibody production as soon as 5 days after the first dose and passive immunity to the neonate as soon as 16 days. The placental IgG transfer ratio increased over time. [58]  Collier et al observed binding, neutralizing, and functional nonneutralizing antibody responses, as well as CD4 and CD8 T-cell responses were present in pregnant, lactating, and nonpregnant women following vaccination. Binding and neutralizing antibodies were also observed in infant cord blood and breast milk. Binding and neutralizing antibody titers against the SARS-CoV-2 B.1.1.7 and B.1.351 variants of concern were reduced, but T-cell responses were preserved against viral variants. [59]

Researchers studied placentas of pregnant women vaccinated with mRNA vaccines after delivery. mRNA vaccines induce an immune response through activation of TLR3, which has been linked to decidual arteriopathy, growth restriction, preterm delivery, and fetal loss in mouse models. Placental examination in women with vaccination showed no increased incidence of decidual arteriopathy, fetal vascular malperfusion, low-grade chronic villitis, or chronic histiocytic intervillositis compared with women in the control group. Incidence of high-grade chronic villitis was higher in the control group than in the vaccinated group. [60]

The American College of Obstetricians and Gynecologists (ACOG) has issued guidelines regarding vaccination of pregnant and lactating patients against COVID-19. Key points from these guidelines are as follows: 

  • Do not withhold COVID-19 vaccines from pregnant women. 
  • Although a conversation with a clinician may be helpful, it should not be required before vaccination, because this may cause unnecessary barriers to access. 
  • COVID-19 vaccines should be offered to lactating individuals on the same basis as they are offered to nonlactating individuals.

Individuals considering COVID-19 vaccination should have access to information about vaccine safety and efficacy, including information about data that are not available. A conversation between the patient and the clinical team providing care may assist with decisions regarding the use of vaccines approved by the FDA under emergency use authorization for the prevention of COVID-19 in pregnant patients. Important considerations include:

  • Level of viral activity in the community
  • Potential efficacy of the vaccine
  • Risk and potential severity of maternal disease, including the effects of disease on the fetus and newborn
  • Safety of the vaccine for the pregnant patient and fetus

Preliminary findings regarding safety of mRNA COVID-19 vaccines in pregnant females from the CDC v-safe registry did not show obvious safety signals. Additional follow-up, including women vaccinated earlier in pregnancy is needed to determine maternal, pregnancy, and infant outcomes.39 Phase 2/3 clinical trials in pregnant women commenced in February 2021 with the BNT162b2 vaccine and the Ad26.COV2.S vaccine is planned for spring 2021.

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