AstraZeneca ChAdOx1 nCoV-19 vaccine does not affect fertility and birth rate outcomes, study says

Within some communities, the coronavirus disease 2019 (COVID-19) vaccine uptake has been affected due to fears of its impact on fertility. This claim has been widespread despite the lack of evidence to support it, low biological plausibility, and data which supports the safety of messenger ribonucleic acid (mRNA) vaccines during pregnancy.

Notably, the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection during pregnancy is a risk factor for severe maternal illness and complications. Therefore, vaccine hesitancy among pregnant or women of childbearing age could have significant public health consequences.

Study: Fertility and birth rate outcomes after ChAdOx1 n-CoV-19 (AZD1222) vaccination. Image Credit: Studio Romantic /

About the study

Researchers from the University of Oxford have recently analyzed pregnancies that have occurred during four ChAdOx1 nCoV-19 clinical trials from three different countries including the United Kingdom, Brazil, and South Africa. All participants were of childbearing age, which is defined as 49 years or younger, and were randomly selected to receive a control vaccine or the ChAdOx1 nCoV-19 vaccine.

Within these trials, the main exclusion criterion was pregnancy; therefore, all of the volunteers provided a negative β-human chorionic gonadotropin (β-hCG) test before vaccination. The pregnancies that occurred following vaccination were recorded and monitored until three months following the birth. The independent data and safety monitoring board reviewed all pregnancy outcomes.

Study findings

Pregnancies were reported in 121 (1%) of the 9,755 participants during these trials. The fertility outcome analysis set included 93 pregnant women, of which 50 had received the ChAdOx1 nCoV-19 vaccine and 43 received the control vaccine.

The pregnancy outcome analysis set included 107 women, of which 72 received the ChAdOx1 nCoV-19 vaccine and 35 received the control vaccine. A pregnancy loss before 23 weeks of gestation was classified as a miscarriage. The baseline characteristics were similar between the two groups, with age and current alcohol use being the biggest variations.

The authors found no evidence of an association between vaccination with ChAdOx1 nCoV-19 and reduced fertility. Women in the control vaccine groups who had received the ChAdOx1 nCoV-19 or another mRNA vaccine as part of a national vaccination program were excluded from the analysis of pregnancy outcomes, which included 11 women vaccinated after unmasking and during pregnancy, and three who had received an mRNA vaccine prior to becoming pregnant.

Notably, there was no increase in the rate of miscarriages in the ChAdOx1 nCoV-19 group when compared to the control group, with a risk ratio of 0.67. Adjusting the analysis for the effect of possible confounders kept the risk ratio below but closer to unity at 0.84. By the time of analysis, 15 live births and three preterm births had occurred in the ChAdOx1 nCoV-19 group. There were no neonatal or stillbirths reported in either group.

The data from Brazil showed that no pregnancy terminations had taken place. However, in Brazil, pregnancy termination is illegal, and uncertainty remains about whether the reports of early pregnancy losses were all actually due to miscarriage. To factor this into the analysis, the authors combined analysis of either termination or miscarriage for all sites, with separate subgroup analyses for miscarriage alone and termination alone, which excludes the data obtained from Brazil.


There was no evidence to suggest that the ChAdOx1 nCoV-19 vaccine has any negative effect on fertility. Furthermore, women who received the ChAdOx1 nCoV-19 vaccine before pregnancy displayed no increase in the risk of miscarriage and no instances of stillbirth when compared to women who received the control vaccine.

With the ever-increasing amount of misinformation regarding SARS-CoV-2 vaccinations, vaccine uptake continues to be affected. However, results such as these and other similar publications can provide evidence to support women in making decisions regarding vaccination.

Journal reference:

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Gemma Wilson

Gemma is a journalism graduate with keen interest in covering business news – specifically startups. She has as a keen eye for technologies and has predicted quite a few successful startups over the last couple of years.

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