News | Large Real-World Study Refutes Claims That Vaccines Cause Infertility
A large study of real-world Swedish population data found no statistical association between COVID-19 vaccination and reduced fertility or delivery outcomes, strongly countering longstanding claims that vaccines affect fertility. The findings were published in Communications Medicine.
Since early in the pandemic, social media has promoted speculation that mRNA vaccines cause infertility, including claims about antibodies against placental proteins. Birth-rate declines amplified these claims, despite epidemiological studies finding no adverse association between vaccination during pregnancy and preterm birth or abnormal fetal development.
Swedish researchers used causal-inference methods approximating randomized comparisons. The study included all 59,773 female residents aged 18–45 in Jönköping County, using regional registers covering about 369,000 people and records of deliveries, vaccination, miscarriage, and death from 2016–2024. Vaccination opened to adults in January 2021, mainly with Comirnaty, Vaxzevria, and Spikevax; boosters followed in September 2021 after the two-dose primary series.
A Cox proportional-hazards model treated vaccination as a time-varying exposure, with estimated conception based on delivery about 280 days later, and adjusted for age. Comorbidities were excluded from the final model because they could introduce bias.
Because delivery records may miss early miscarriage, a separate miscarriage analysis was conducted. Loss at 22 weeks or later was defined as stillbirth. A sensitivity analysis assumed an average pregnancy of 266 days.
Overall, 75.5% completed primary vaccination and 97% of them received mRNA vaccines. Delivery rates fell by 8%, 4%, and 3% from 2021–2024. About 10% delivered before a booster, and about 1% miscarried during the vaccination period.
Vaccination was not significantly associated with delivery rates; adjusted hazard ratios were near 1 and confidence intervals crossed the null value. Neither primary nor sensitivity analyses found an association with miscarriage.
The authors said lockdown-related behavior, economic uncertainty, and changing reproductive intentions were more plausible causes of lower births. Sweden’s birth rate had already fallen in the 1990s, reducing the current population at peak reproductive age. Median parental age for births in 2021–2024 was 31, showing that the pool of potential parents had shrunk before vaccines existed.
The authors cautioned that identifying pregnancies through delivery records may introduce selection bias and underestimate unregistered early losses, but would not change the main conclusion.
Using nationally representative real-world data, the study strengthens vaccine-safety evidence and supports public-health communication correcting fertility misinformation.
News | Large Real-World Study Refutes Claims That Vaccines Cause Infertility
News | Large Real-World Study Refutes Claims That Vaccines Cause Infertility
A large study of real-world Swedish population data found no statistical association between COVID-19 vaccination and reduced fertility or delivery outcomes, strongly countering longstanding claims that vaccines affect fertility. The findings were published in Communications Medicine.
Since early in the pandemic, social media has promoted speculation that mRNA vaccines cause infertility, including claims about antibodies against placental proteins. Birth-rate declines amplified these claims, despite epidemiological studies finding no adverse association between vaccination during pregnancy and preterm birth or abnormal fetal development.
Swedish researchers used causal-inference methods approximating randomized comparisons. The study included all 59,773 female residents aged 18–45 in Jönköping County, using regional registers covering about 369,000 people and records of deliveries, vaccination, miscarriage, and death from 2016–2024. Vaccination opened to adults in January 2021, mainly with Comirnaty, Vaxzevria, and Spikevax; boosters followed in September 2021 after the two-dose primary series.
A Cox proportional-hazards model treated vaccination as a time-varying exposure, with estimated conception based on delivery about 280 days later, and adjusted for age. Comorbidities were excluded from the final model because they could introduce bias.
Because delivery records may miss early miscarriage, a separate miscarriage analysis was conducted. Loss at 22 weeks or later was defined as stillbirth. A sensitivity analysis assumed an average pregnancy of 266 days.
Overall, 75.5% completed primary vaccination and 97% of them received mRNA vaccines. Delivery rates fell by 8%, 4%, and 3% from 2021–2024. About 10% delivered before a booster, and about 1% miscarried during the vaccination period.
Vaccination was not significantly associated with delivery rates; adjusted hazard ratios were near 1 and confidence intervals crossed the null value. Neither primary nor sensitivity analyses found an association with miscarriage.
The authors said lockdown-related behavior, economic uncertainty, and changing reproductive intentions were more plausible causes of lower births. Sweden’s birth rate had already fallen in the 1990s, reducing the current population at peak reproductive age. Median parental age for births in 2021–2024 was 31, showing that the pool of potential parents had shrunk before vaccines existed.
The authors cautioned that identifying pregnancies through delivery records may introduce selection bias and underestimate unregistered early losses, but would not change the main conclusion.
Using nationally representative real-world data, the study strengthens vaccine-safety evidence and supports public-health communication correcting fertility misinformation.
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