Neither mRNA nor inactivated virus COVID-19 vaccines cause changes to syncytin-1 antibody levels in women of reproductive age, researchers at Yale School of Medicine, Connecticut, have shown.
Claims made online that COVID-19 vaccines could affect fertility due to the induction of syncytin-1 antibodies, which inhibit placental formation, have been blamed for low vaccine uptake rates among pregnant women (see BioNews 1104). Now a study designed specifically to tackle this claim has found no difference in syncytin-1 antibody levels in women who had been vaccinated against COVID-19 compared to those that had not.
'The findings provide further evidence that existing mRNA vaccines are safe for pregnant women and those planning to become pregnant' said Professor Akiko Iwasaki, Sterling professor of immunobiology and of molecular, cellular and developmental biology at Yale University
Claims that COVID-19 vaccination could cause an immune reaction against syncytin-1, a protein responsible for placenta formation during embryo formation, originally appeared after a letter was sent to the European Medicines Agency asking it to stop emergency authorisation of mRNA vaccines. It included an assertation that there was no evidence that antibodies against spike proteins, which might be structurally similar to syncytin-1 antibodies, wouldn't impair the formation of the placenta and prevent pregnancy.
To examine this claim Professor Iwasaki and her group compared the levels of syncytin-1 antibodies in two independent cohorts of women under the age of 60: one group vaccinated with Pfizer BioNTech or Moderna mRNA vaccines or the CoronaVac inactivated virus vaccine, and the other unvaccinated. They measured syncytin-1 antibodies before vaccination, between vaccines and after vaccination. No elevated levels of the antibody were observed in the vaccinated women compared to those unvaccinated.
To counter claims the COVID-19 vaccine can affect fetal development, the authors compared the size, weight and presence of congenital defects of mice born to female mice vaccinated early on in their pregnancy, with those born to unvaccinated mothers.
No overt maternal illnesses were observed in either the vaccinated or unvaccinated mice while there were no discernable differences in fetal size and weight of mice born to vaccinated or unvaccinated mothers.
'Unvaccinated pregnant women are at increased risk for severe consequences of COVID-19 infections, including hospitalisation and intensive care stays than unvaccinated pregnant women, and face increased risk of delivering a preterm or stillborn infant.' Professor Iwasaki said.