A large-scale study analyzing national data in the Czech Republic has found lower rates of successful conceptions (live births) among women vaccinated against COVID-19 compared to their unvaccinated peers. Researchers reviewed monthly vaccinations and birth records for approximately 1.3 million women aged 18–39 from January 2021 to December 2023. The study reports that conception rates per 1,000 women were significantly lower among vaccinated women, approximately 1.5 times higher among unvaccinated women during much of that period.
The authors note the findings are observational and hypothesis-generating, acknowledging the study does not establish causation. Possible confounders include behavioral factors such as vaccination timing relative to pregnancy planning. Leading fertility and public health experts stress these results require further analysis before drawing firm conclusions.
Earlier Czech research measuring hormone and fertility markers in 25 women showed no significant changes after vaccination. Other international reviews—including from Swissmedic and AMA—have found no evidence that COVID-19 vaccines impair fertility, although temporary menstrual cycle changes have been reported.
A comprehensive demographic modeling study also identified a decline in the overall fertility rate (TFR) in Czechia from 1.83 children per woman in 2021 to 1.62 in 2022. It noted the timing corresponded with the vaccine rollout but attributed the decline to multiple factors, including economic uncertainty and delayed conception rather than a direct vaccine effect.
