During the rise of the COVID-19 Omicron variant, infants under 6 months of age (who were ineligible for vaccination) were especially vulnerable to hospitalization. The Omicron surge saw infant rates of hospitalization climb above those of older groups at the time, such as children, adolescents, and adults under the age of 65.

According to a recent study published in Vaccine, getting the COVID-19 booster shot on top of the initial mRNA vaccine leads to a dramatic increase in antibodies—for mothers and infants—at the time of delivery.1

Receiving the COVID-19 vaccine during pregnancy is cited as crucial for both confronting disproportionate infant vulnerability and easing the disease burden for new and expecting mothers, the study authors noted. Previous studies have demonstrated that vaccine-induced antibodies can be transferred to an infant through the placenta to reduce disease risks in the infant’s first 6 months.

A total of 240 pregnant participants were examined between July 6, 2021 and January 1, 2022. At any time over the course of their pregnancy, they received a primary 2-dose series of the Moderna mRNA-1273 (Moderna) or Pfizer-BioNTech (Pfizer) COVID-19 vaccine, or a single booster does of either.

Researchers derived antibody assay sera from maternal blood collected pre- and post-vaccination; maternal and cord blood were also taken at the time of delivery to compare booster recipients to those who did not receive the booster. Participants had a median age of 34 years and were followed for the next 12 months after delivery.

Binding of immunoglobulin G (IgG) to the receptor binding domain (RBD) and full-length Spike were measured and reported as binding antibody units (BAU/mL). Furthermore, the presence of SARS-CoV-2 neutralizing antibodies (nAb) was assessed with a pseudovirus neutralizing assay as well as a live virus focus reduction neutralization titer (FRNT) assay (which contained viruses representing the D6146 SARS-CoV-2 mutation, as well as Omicron BA.1 and Delta variants). To calculate transplacental antibody transferring, the antibody ratios were measured in cord and maternal blood at delivery.

At delivery, the post-vaccine antibody levels were significantly higher in booster recipients compared with pregnant individuals who only went through the primary 2-dose vaccine series. Booster recipients registered mean levels of 2201 BAU/mL, which was more than 9 times higher than individuals who received 2 doses of Pfizer, and almost 5 times higher than Moderna 2-dose recipients.

The booster vaccine also exhibited significantly higher levels of spike IgG in cord blood (3290 BAU/mL) compared with levels resulting from Pfizer (369 BAU/mL, almost 9 times lower) and Moderna (729 BAU/mL, over 4 times lower) vaccinations, respectively. The authors witnessed similar results regarding RBD IgG in cord blood.

In a concurrent trend, post-vaccination nAb levels were drastically higher in booster recipients. Live virus nAb levels were detectable in 100% of those who were boosted compared to 96% and 68% in Moderna and Pfizer 2-dose individuals. Regarding the Omicron BA.1 live virus nAb levels, 73% of boosted participants presented with these titers compared to 22% of Moderna recipients and 9% of Pfizer, respectively. Researchers noted that transplacental antibody transfer levels registered efficiently across all members.

After SARS-CoV-2 infection, pregnant individuals are more vulnerable to obstetric complications and severe disease. After receiving the mRNA COVID-19 vaccines, “robust antibody responses” were observed in pregnant participants. Additionally, infants exhibited an effective reception of antibodies in this study. While benefits were observed across all groups, the findings here bolster evidence arguing the benefits of receiving the booster vaccine during pregnancy. Considering these results, the researchers call for future studies to associate more deeply how COVID-19 vaccine usage impacts maternal and infant outcomes.

This article originally appeared on AJMC.

1. 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. Published online June 13, 2023. doi: 10.1016/j.vaccine.2023.06.032