Receiving SARS-CoV-2 Booster During Pregnancy May Improve Newborn’s Immune Responses to Virus


A COVID-19 booster dose increased both maternal and cord blood binding and neutralizing antibody levels against virus strains, including Omicron BA.1.

Pregnant individuals who become infected with SARS-CoV-2 are at a higher risk of severe disease and obstetric complications. Additionally, infants younger than 6 months of age are at a higher risk of hospitalization when infected with SARS-CoV-2 due to their ineligibility to get vaccinated, particularly during the surge of Omicron variants (BA.1, BA.4, and BA.5).

Woman receiving vaccination | Prostock-studio |

Woman receiving vaccination | Prostock-studio |

From July 2021 to January 2022, researchers conducted a prospective, multicenter cohort study of participants vaccinated during pregnancy with either primary or booster mRNA COVID-19 vaccines. Investigators evaluated the binding and neutralizing antibody (nAb) response to COVID-19 mRNA vaccines in pregnant mothers and on transplacental antibody levels in the newborn to define the functional immune response to Omicron in these groups.

SARS-CoV-2 nAb titers were evaluated by a pseudovirus-neutralizing test using replication-incompetent lentivirus coding for luciferase and containing the SARS-CoV-2 full-length spike protein in the viral envelope, as well as a live virus focus reduction neutralization titer test with viruses representing SARS-CoV-2 spike mutation D614G and Delta and Omicron BA.1 variants.

A total of 240 participants who were pregnant with and without medical comorbidities, each received a primary 2-dose series of the Pfizer-BioNTech (Pfizer) or Moderna mRNA-1273 (Moderna) vaccine, or a monovalent booster dose of either vaccine at any time during pregnancy, as per the recommendations. Pre- and post-vaccination (from 2 weeks post-vaccination to delivery), maternal blood samples were collected from the participants, and maternal and cord blood were collected at delivery.

Of the 240 participants who were pregnant and gave birth, 100 (102 infants) received Pfizer, 67 (68 infants) received Moderna, and 73 (75 infants) received a booster dose, with booster doses being primarily homologous with the primary series (80.8%). Participants had completed their primary 2-dose series at a median 17.1 weeks of gestation, whereas booster vaccination was received at a median of 28.6 weeks.

The considerable increase in binding and nAb titers measured in both mothers and newborns at the time of delivery and post-booster vaccination strongly supports the administration of COVID-19 booster doses during pregnancy. In addition to the D614G vaccine strain, this was also evident in the nAb response to both Delta and Omicron BA.1, which showed much higher levels in booster recipients and in cord blood at the time of delivery.

Similar to other research, maternal binding IgG antibodies against spike and RBD SARS-CoV-2 proteins were efficiently transferred through the placenta and concentrated in the infant, which is significant given high hospital rates among infants <6 months of age due to the Omicron BA.1 and BA.5 surges. Transplacental antibody transfer is the key component of newborn protection from SARS-CoV-2 infection.

Study findings show support for the use of a booster dose of COVID-19 vaccine during pregnancy, particularly among those who have already completed their primary series of vaccinations prior to or early on in pregnancy. COVID-19 mRNA vaccination during pregnancy had caused an apparent immune response in mothers and efficient transplacental antibody transfer to the newborn.

Previous research reported higher IgG responses in pregnant women who had received a booster dose compared to women who only received 2 doses of the vaccine. The current study’s findings included pseudo- and live nAb data, which confirm the functional activity and the antibodies’ potential protective effects on the newborn, according to the authors.

The current study demonstrates that a booster dose during pregnancy had significantly increased maternal and cord blood binding and neutralizing antibody levels, including against Omicron BA.1. At delivery, live virus nAb to Omicron BA.1 were present in 9% of Pfizer primary series recipients and 22% of Moderna primary series recipients, and in 73% of boosted participants; however, titers were noticeably lower compared to the D614G strain. Transplacental antibody transfer was effective for all regimens with median transfer ratio range (1.55–1.77 for IgG, 1.00–1.78 for live virus nAb, and 1.79–2.36 for pseudovirus nAb).

Given the trial’s observational design, the timing of vaccination during pregnancy was not pre-specified. Further, results are limited to the evaluation of mRNA vaccines depending on the availability and recommendations within the United States. The study authors suggest that additional research should be performed to better demonstrate the immune response following administration with other maternal vaccines, as well as the maternal health status’s influence.


Munoz FM, Posavad CM, Richardson BA, et al. COVID-19 booster vaccination during pregnancy enhances maternal binding and neutralizing antibody responses and transplacental antibody transfer to the newborn. Vaccine. 2023;41(36):5296-5303. doi:10.1016/j.vaccine.2023.06.032.

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