Dr. Philp McMillan, John McMillan
In the late 1950s, doctors prescribed a new drug to pregnant women suffering from morning sickness. Thalidomide was marketed as completely safe, a breakthrough in prenatal care. Women trusted their physicians and the pharmaceutical companies’ assurances. Yet, within years, over 10,000 children were born with severe birth defects: missing limbs, malformed organs, devastating disabilities. The drug had never been tested for reproductive safety. This tragedy established an inviolable principle in medicine: new medical interventions require extensive reproductive safety data before widespread use in women of childbearing age. The burden of proof must demonstrate safety, not assume it.
Alarming Fertility Signals
Recent data from the Czech Republic raises questions about whether this principle was upheld during the global COVID-19 response. In 2025, the Czech Statistical Office released the first major population-level analysis examining fertility outcomes by vaccination status. The study tracked 1.3 million women aged 18–39 from January 2021 through March 2023. Researchers calculated “successful conceptions,” meaning pregnancies resulting in live births, comparing rates between vaccinated and unvaccinated women.
The findings were disturbing. From June 2021 onward, unvaccinated women showed conception rates of approximately six per 1,000 women. Vaccinated women showed rates of four per 1,000, and these differences persisted throughout the study period. The Czech Republic’s total fertility rate dropped from 1.83 births per woman in 2021 to 1.45 in 2023. Similar declines have been observed around the same period in countries ranging from Germany to Taiwan.
Explaining The Infertility Spike
Researchers point to several biological mechanisms that might explain these patterns. The COVID-19 spike protein, whether from infection or vaccination, may be triggering autoimmune responses affecting reproductive organs. Studies have documented menstrual irregularities in up to 44 percent of women following vaccination. Research has also shown temporary reductions in sperm concentration and motility in men.
In other words, a vaccinated woman could face reduced egg release, while a vaccinated man might produce sperm that look normal but do not function properly. Even unvaccinated women partnered with vaccinated men could experience lower conception rates.
Another theory is that the spike protein interacts with ACE2 receptors found throughout reproductive tissues. This may interfere with hormone signaling necessary for ovulation and implantation. These mechanisms remain theoretical but align with observed population trends.
Dr. Philip McMillan, a researcher and clinician who has studied COVID-19 and autoimmunity since 2020, draws parallels to historical medical oversights. “Essentially, what I’m doing here is the equivalent of pulling me back to 1970, seeing everybody smoking and me saying, you know, you’re going to see a lot of COPD and cancer in the next decade or two.”
The Czech researchers acknowledge their study’s limitations. Association does not prove causation. Vaccinated and unvaccinated women may differ in unmeasured ways: age distribution within the 18–39 range, socioeconomic factors, health behaviors. Some unvaccinated women may have actively planned pregnancies while avoiding vaccination.
Yet the researchers note that deferring vaccination contradicted official Czech health recommendations. If self-selection fully explained the fertility gap, total population fertility should have remained stable. Instead, it declined sharply.
The Urgent Need for Answers
Despite these alarming results being publicly known, the persistence of vaccine mandates has created ethical concerns. Young women of childbearing age represent one of the lowest-risk demographics for severe COVID-19 outcomes. They were also the group most likely to experience reproductive consequences from any intervention affecting hormonal systems. The risk-benefit calculation for this population differed dramatically from elderly or immunocompromised individuals. As of February 2025, several U.S. colleges still mandated COVID-19 vaccination, despite young women facing minimal risk from severe COVID-19. Institutions in California, Georgia, New Hampshire, Ohio, Oregon, and Pennsylvania maintained these requirements until federal funding restrictions forced them to reconsider.
The Czech study authors conclude their findings with a “call for further studies of the potential influence of COVID-19 vaccination on human fecundability and fertility.” They stress their research represents hypothesis-generating evidence, not definitive proof. But if vaccination reduces conception rates by even a fraction of what the Czech data suggests, the implications for global demographics are profound. Falling birth rates already strain social systems designed around population growth. Further fertility decline could accelerate these challenges.
The medical establishment faces a choice. It can wait for definitive proof while potentially affected couples struggle with conception. Or it can investigate these signals proactively, as the hard-won lessons of Thalidomide demand. Another example of reproductive risks taking years to emerge is the drug Diethylstilbestrol (DES), prescribed to prevent miscarriage from the 1940s through the 1970s. It caused no immediate problems. A generation later, daughters of women who took DES developed rare vaginal cancers and fertility problems. Young women considering vaccination deserve full disclosure about unknowns regarding long-term reproductive effects. The principle established by the Thalidomide tragedy, that reproductive safety requires affirmative proof, applies equally today.
The Czech data represents one study from one country. Long-term follow-up across diverse populations is needed to track outcomes beyond immediate conception rates. Until such research emerges, uncertainty persists. For potential parents, for physicians counseling patients, for policymakers crafting health guidelines, the Czech findings raise questions that need answers. The health of future generations may depend on how seriously we take these early signals.
The history of medicine teaches humility. Time and again, interventions deemed safe in their time have had unexpected consequences years later. The Czech conception data may prove to be a statistical anomaly, explained by factors not yet identified, or it may represent a forewarning of population crisis. Time will tell. But with birth rates falling, and a growing body of signals linking immune activity to fertility, this is not a conversation we can long afford to postpone.
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