The rate of successful conception — a pregnancy leading to live birth nine months later — for women who received the COVID-19 vaccine was “substantially lower” than for unvaccinated women, according to a new peer-reviewed study published last week in the International Journal of Risk & Safety in Medicine.
JUNE 27, 2025
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The rate of successful conception — a pregnancy leading to live birth nine months later — for women who received the COVID-19 vaccine was “substantially lower” than for unvaccinated women, according to a new peer-reviewed study.
Brian Hooker, Ph.D., chief scientific officer for Children’s Health Defense (CHD), called the study’s conclusions alarming. He said:
“This preliminary analysis shows that much more information is needed to understand both short- and long-term implications of the different types of COVID shots on fertility and pregnancy parameters. This information should have been obtained prior to any public use of the COVID vaccine.”
The results showed that by June 2021, approximately six months after COVID-19 vaccines became available to the public, successful conceptions per 1,000 women were considerably lower for vaccinated women than for those not vaccinated.
The researchers observed an increase in the rate of successful conceptions for unvaccinated women beginning in June 2021, which “was maintained over the subsequent 6-month period.”
In 2022, the rate of successful conceptions “stabilized” among both vaccinated and unvaccinated women but remained “about 1.5 times higher” for the latter group.
‘Troubling’ results indicate long-term impact on reproductive health
The preliminary analysis, by five researchers from the Czech Republic, Denmark and Sweden, was published last week in the International Journal of Risk & Safety in Medicine.
The study examined data obtained from the Czech Republic, one of the few countries where nationwide birth data for women who were vaccinated or unvaccinated for COVID-19 are available, the authors said.
The researchers analyzed data on 1.3 million women, ages 18-39, between January 2021 and December 2023.
The authors said their reasons for undertaking the study included existing research showing that COVID-19 vaccines have adverse effects on “menstrual characteristics,” and the lack of data on the effect of COVID-19 vaccines on birth rates.
Data from several countries had shown decreased birth rates during the COVID-19 pandemic, researchers said. However, the “potential influence of COVID-19 vaccines on reproductive health was not assessed” in randomized preauthorization trials for those vaccines.
Pediatrician Dr. Michelle Perro said the study’s findings are “deeply concerning” and “provide insight regarding adverse effects on fertility that warrants immediate and unbiased scientific investigation.”
“Releasing a new technology, especially one administered to our most vulnerable populations without comprehensive, long-term safety data, once again, has been shown to be disastrous towards the health of future generations,” Perro said.
Karl Jablonowski, Ph.D., senior research scientist at CHD, said it was “troubling” that the rates of successful conceptions among vaccinated and unvaccinated women have not converged after 2021, indicating the vaccines’ potentially long-term impact on women’s reproductive health.
“If the exposure had short-term influence, the two groups would converge over time, and they don’t,” Jablonowski said.
Among the vaccinated women examined in the study, 96% received either the Pfizer-BioNTech or Moderna vaccines, with 11 times more women receiving Pfizer’s vaccine compared to Moderna’s.
Multiple studies link COVID vaccines and reproductive problems
The researchers noted the relationship between vaccination and fertility is not necessarily causal, and some women may have based their decision to get vaccinated on whether they planned to become pregnant — a possible example of “self-selection bias.”
However, the researchers pointed out that, during the pandemic, the overall fertility rate in the Czech Republic declined. During that time, Czech public health authorities recommended that pregnant women get vaccinated — a recommendation the researchers said many women likely followed.
These factors reduce the likelihood that self-selection bias accounts for the difference in successful conception rates among vaccinated and unvaccinated women.
Other recent studies have also found an association between COVID-19 vaccines and reproductive problems.
A peer-reviewed study published in BMC Pregnancy and Childbirth in April found that among pregnant women who tested positive for COVID-19, those who received a COVID-19 vaccine were significantly more likely to miscarry compared to unvaccinated women.
A peer-reviewed study published in March in the journal Vaccines found that COVID-19 vaccines decreased the number of primordial follicles — “the foundation of fertility” — in female rats by up to 60%.
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Contaminated COVID vaccine batches may have lowered conception rates
According to the Czech researchers, highly contaminated early batches of COVID-19 vaccines may be related to decreased rates of successful conception — a theory they said deserves further investigation.
The researchers cited several studies — including a peer-reviewed analysis by Jablonowski and Hooker published last year in the journal Science, Public Health Policy and the Law — that found early batches of COVID-19 vaccines led to a disproportionately higher number of adverse events.
According to the Jablonowski-Hooker analysis, batches of the Pfizer-BioNTech COVID-19 vaccine distributed in the U.S. were associated with significantly different rates of serious adverse events.
Α 2023 Danish study found a significant percentage of the batches of the Pfizer-BioNTech BNT162b2 COVID-19 vaccine distributed in the European Union likely consisted of placebos — and the non-placebo batches demonstrated higher-than-normal severe adverse events in recipients.
In a paper published in the journal Medicine last year, the authors of the Danish study expanded their analysis to Sweden, finding the existence of the same batch-dependent issues in that country.
In another study published last year, researchers from the Czech Republic replicated the Danish study’s methodology. They found that COVID-19 vaccine batches in that country also had differing rates of adverse events, with more issues seen in early vaccine releases for all vaccines.
The lead author of that paper, Tomáš Fürst, Ph.D., is one of the new study’s co-authors.
Perro said the study’s findings “highlight the necessity for extreme caution in public health interventions, particularly for women of childbearing age and children when they involve reproductive health.” She supports calls for the “immediate cessation and withdrawal of mRNA technology.”
Hooker said, “Any decrease in fertility and increase in miscarriages and stillbirths lies at the heart of the fact that this vaccine technology should have never been rolled out to the public in the first place.”Related articles in The Defender
- COVID Vaccines May Reduce Women’s Lifelong Egg Supply, Rat Study Suggests
- Another Study Shows Higher Miscarriage Rate Among Women Who Received COVID Vaccines
- Watch: Naomi Wolf Discusses ‘Chilling’ Revelations From Pfizer Documents
- CHD Scientists Uncover Evidence of Pfizer ‘Hot Lots’ Linked to Higher Rates of COVID Vaccine Injuries
- ‘Bombshell’ Study of Pfizer COVID Vaccine Suggests Some People Got Highly Dangerous Shots, Others Got a Placebo
Michael Nevradakis, Ph.D.
Michael Nevradakis, Ph.D., based in Athens, Greece, is a senior reporter for The Defender and host of “The Defender In-Depth” on CHD.TV.
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