Pregnant women are at high risk for severe COVID-19 infection and death. Yet, insufficient safety data on babies has led many guidelines to leave the decision-making and potential threats to future mothers. While the vaccine trials did not directly test pregnant women, more real-world data suggests the vaccine may provide immunity benefits to newborns through breastmilk.
In Israel, there has been an aggressive vaccine distribution campaign with a majority of the population vaccinated. Israel’s vaccination efforts have led it to become a case study for vaccine effects on multiple populations.
Now new research led by Michal Kovo from The Hebrew University of Jerusalem suggests fetuses also benefit from vaccination. They found pregnant mothers who developed neutralizing antibodies specific to the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) produced from the Pfizer vaccine could be transferred to the fetus.
The researchers write:
The study “Maternal to Neonatal transfer of SARS-CoV-2 and BNT162b2 antibodies” is available as a preprint on the medRxiv* server, while the article undergoes peer review.
How they did it
The study took place across 8 Israel hospitals starting in April 2020. Pregnant women needed to be at least 18 years and were being admitted for delivery. Women who actively had COVID-19 illness were excluded.
A total of 1,094 pregnant women were included in the study and divided into three groups. Women with prior COVID-19 infection were in the vaccinated group, women with prior infection were in the unvaccinated group. Pregnant women with no documentation of COVID-19 illness were assigned the control group.
Researchers collected maternal and fetal blood samples along with the umbilical cord from all patients before delivery.
Increased fetal antibody transmission when infected mid-pregnancy
Blood samples showed pregnant women who were positive for SARS-CoV-2 before week 30 had higher transmission levels of IgG specific to the S1, S2, RBD, and N antigens compared to women who were infected after week 30.
Among 65 pregnant women with a history of COVID-19 infection, the top 90% were seropositive with an IgG response for N antigens. In contrast, 14% of the control group were considered seropositive, indicating a preexisting induced immunity due to infection. About 8% of vaccinated women were seropositive for N, of which three had tested positive for SARS-CoV-2.