When the Moderna COVID-19 vaccine is administered to pregnant mice, it crosses the placenta and enters the fetus, according to a study about to be published in a peer-reviewed journal. The study adds to existing evidence that the vaccines aren’t safe for pregnant women.
by Brenda Baletti, Ph.D. The Defender
This article was originally published by The Defender—Childrens Health Defense News & Views Website on February 20, 2025.
When the Moderna COVID-19 vaccine is administered to pregnant mice, it crosses the placenta and enters the fetus, according to a study about to be published in the peer-reviewed journal Molecular Therapy Nucleic Acids.
“This study provides the first in vivo confirmation that mRNA injections cross the placenta, directly reaching the fetus,” Nicolas Hulscher, who first reported the study, wrote on Substack.
“It also helps explain why these genetic injections pose such serious risks to pregnant women and their unborn children,” he added.
Karl Jablonowski, Ph.D., senior research scientist at Children’s Health Defense, said that if the U.S. Food and Drug Administration and the Centers for Disease Control and Prevention accept this study as “reflective of medical reality, they must immediately revoke their approvals and recommendations on all lipid nanoparticle (LNP)-encased mRNA vaccines and therapeutics during pregnancy.”
The study authors, from Chang Gung University and Memorial Hospital in Taiwan, said they conducted the study because although administration of the COVID-19 vaccine to pregnant women has been “generally recognized as safe,” whether and how the drug passes the placental barrier “remains shrouded in clouds.”
The dominant theory has been that administering a COVID-19 shot to a mother during pregnancy protects her and confers protection to her fetus—a “two for the price of one” approach —by transferring anti-spike antibodies through the placenta rather than transferring the vaccine mRNA or the mRNA decoded spike protein itself.
This mechanism is how traditional vaccines, like Tdap (tetanus, diphtheria, acellular pertussis), work.
Based on that theory, Jablonowski said, “Pregnant mothers are encouraged to get vaccines, so they can create antibodies against the pathogens, and pass those antibodies through the placental barrier. “
However, mRNA vaccines work differently than traditional vaccines. The researchers set out to assess whether the COVID-19 vaccine itself could cross the placenta.
They conducted their investigation using mRNA-1273, Moderna’s Spikevax vaccine, in mice. Due to certain similar placental characteristics, mouse studies provide good models for simulating similar phenomena in humans.
The researchers found that the vaccine rapidly crossed the placenta in mice, prompting the need to reevaluate the ability of the vaccine to cross the placenta in humans and better understand the immune response of fetuses or infants exposed to maternal mRNA vaccination.
“The information obtained will have a profound influence on the COVID-19 vaccination strategy in infants born to gestationally-vaccinated mothers,” they wrote.
Jablonowski said the implications of the findings were significant.
“In theory, the placental barrier protects the fetus from the vaccine ingredients,” he said. “The authors demonstrate that this theory is obliterated with Moderna’s mRNA COVID-19 vaccine.”
mRNA crosses the placenta and persists for weeks in fetus
The authors said that at least one previous major study detected neither mRNA nor the SARS-CoV-2 spike protein in the placenta and cord blood sampled after maternal human vaccination.
That led researchers to conclude the placenta acted as a natural barrier to the lipid nanoparticles (LNPs) that carry the mRNA throughout a vaccinated mother’s body, “providing additional reassurance about the safety of mRNA vaccines during pregnancy.”
However, they wrote, other research indicated that if the mRNA did cross the placental barrier, it would do so quickly—in the first 24 hours—and therefore may not be detectable in the placenta and cord blood. And animal studies showed fetuses that received the LNPs intravenously showed rapid systemic spread.
These findings raised doubts about the claim that the vaccine wasn’t crossing the placental barrier just because it wasn’t found in fetal blood or the placenta.
To test their theory, the researchers administered the Moderna vaccine to pregnant mice via intramuscular injection. They tested different vaccine doses. The fetuses were delivered at different selected times to test for how long traces of mRNA persisted.
They tested fetal tissue and placentas for the presence of LNPs, the spike mRNA protein, anti-spike serums and other markers of immunogenicity.
They found that the mRNA vaccine passed the placental barrier rapidly, within one hour of maternal vaccination. The mRNA and the LNP carriers persisted in fetal blood and tissue—primarily in the liver—even after they had cleared from maternal circulation. They also found the mRNA persisted in fetal liver and spleen for at least three weeks after the mouse pups were born.
Fetal tissues also actively translated the vaccine mRNA into the spike protein in the pups’ bodies. This raises concerns about unintended immune response or long-term biological effects, according to Hulscher.
Jablonowski said that specifically, the manufacturing process of the SARS-CoV-2 LNP vaccines has not been able to eliminate DNA contamination—and the LNP drives that contamination directly into the cell.
“During the rapid development of the fetus is a vulnerable time for fetal cells to be combating foreign DNA contamination,” he said.
Researchers celebrate possibility for new mRNA applications, critics say that suggestion is ‘outright reckless’
The researchers said the vaccine “did not pose discernable safety issues in pregnant mice and their pups.” However, they conceded, “the risk of long-term genotoxicity in the offspring born to mRNA-vaccinated mothers cannot be overlooked.”
That said, the researchers also concluded that it may be a good thing that mRNA vaccines can pass quickly and directly through the placenta because it opens the door to new biotechnological applications.
For example, it creates a prospect of using mRNA-LNP technology as prenatal mRNA therapies for genetic diseases, and “broaden[s] our horizons of prenatal mRNA therapeutics.”
Commenting on those conclusions Jablonowski said, “While I can maintain respect for the scientists doing the science, I cannot respect their conclusions. I find their posturing on fetal vaccination to be outright reckless,” he said. This article was originally published by The Defender—Children Health Defense News & Views Website under Creative Commons license CC BYNC-ND 4.0
