A new study from the Czech Republic published last week found that the rate of successful conceptions resulting in the live birth of a child was “substantially lower” for women vaccinated against COVID-19 compared with unvaccinated women, based on nationwide data.
“We conclude that at least from June 2021, SC [successful conception] rates in the Czech Republic for women vaccinated against COVID-19 before SC were substantially lower than for those who were unvaccinated before SC. These hypothesis-generating and preliminary results call for further studies of the influence of COVID-19 vaccination on human fecundability and fertility,” said the researchers.
The study examined data on women aged between 18-39 years across the Czech Republic between 2021 and 2023, including approximately 1.3 million women. It found that the successful conception rate for unvaccinated women was a substantial 1.5 times higher than the rate for vaccinated women.
The successful conception rate for vaccinated women was also lower than the expected level based on the proportion of the population that was vaccinated.
Researchers highlighted a previous study conducted in the U.S. and Canada that showed no reduction in successful conception rates for vaccinated women, but pointed out that the earlier study had a drastically lower sample size, relied on self-reported vaccination status, and only included women actively trying to become pregnant.
Czech researchers argued that the strength of their study was its broad review of the overall population of fertile women, something they believe had not been studied previously in the context of COVID vaccination.
“Our current real-world population data from the Czech Republic indicated that COVID-19 vaccination was associated with a substantial and sustained decrease in SC rate compared to non-vaccinated women,” said researchers.
They pointed out that the correlation between lower fertility and vaccination status does not necessarily imply causation, citing objections suggesting that women intending to become pregnant could have been less likely to receive the vaccine.
Researchers dismissed that objection. They argued that if that were the case, the country would not have seen an overall decline in successful conceptions after a large percentage of the population became vaccinated.
“If this type of self-selection bias had been the predominant underlying factor for the observed reduction in SC rates in vaccinated women, the total fertility rate for the entire population would have remained relatively constant throughout the study period,” said the researchers.
In reality, however, the country saw a drastic fertility drop, from 1.83 births per 1,000 women in 2021 to just 1.45 in 2023.
