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expert reaction to two papers from earlier this week looking at rates of miscarriage in women who had and hadn’t received COVID-19 vaccines

Two papers published on Wednesday in The Journal of the American Medical Association (JAMA) and in The New England Journal of Medicine (NEJM) look at rates of spontaneous abortion in women who had and hadn’t received COVID-19 vaccines.


Prof Penny Ward, Independent Pharmaceutical Physician, Visiting Professor in Pharmaceutical Medicine at King’s College London, said:

“The small study published in JAMA used data from large healthcare databases in the USA to compare the odds of receiving a COVID-19 vaccine in the 28 days prior to a spontaneous abortion (miscarriage within the first 20 weeks of pregnancy) compared with the odds of receiving a COVID-19 vaccine in the 28 days prior to index dates for ongoing pregnancies.  The comparison found no significant difference between these two groups, suggesting that COVID mRNA vaccine is not associated with miscarriage.  Although the ‘point estimate’ (that is the odds of having had a vaccine within 4 weeks prior to a miscarriage) is in general more than 1 (i.e. more likely) when gestational age, maternal age and ongoing antenatal care were adjusted for, the 95% confidence limits cross 1 (i.e. range from less to more than 1) so the finding is not statistically different.

“This lack of association between COVID mRNA vaccine and miscarriage is further confirmed by a second report (in the NEJM) from 2456 women enrolled in an ongoing pregnancy registry study assessing cumulative probability of miscarriage in pregnant women that had received a covid vaccine.  Pregnancy registries are tried and trusted methods for assessing the impact of medicines on pregnancy outcomes and have been used for many years.  This second study confirmed that the cumulative risk of miscarriage in the vaccinated population is the same as that reported from non vaccinated women in earlier work.

“Taken together these studies provide reassuring support for the safety of the mRNA vaccines in pregnancy.”



JAMA research letter: ‘Spontaneous Abortion Following COVID-19 Vaccination During Pregnancy’ by Elyse O. Kharbanda et al. was published in JAMA on Wednesday 8 September 2021.

DOI: 10.1001/jama.2021.15494

NEJM Correspondence paper: ‘Receipt of mRNA Covid-19 Vaccines and Risk of Spontaneous Abortion’ by Lauren H. Zauche et al. was published in the New England Journal of Medicine on Wednesday 8 September 2021.

DOI: 10.1056/NEJMc2113891



All our previous output on this subject can be seen at this weblink:



Declared interests

Dr Penny Ward: “No COIs. I am semi-retired, but I am owner/Director of PWG Consulting (Biopharma) Ltd a consulting firm advising companies on drug and device development. Between December 2016 and July 2019 I served as Chief Medical Officer of Virion Biotherapeutics Ltd, a company developing antiviral treatments for respiratory viral diseases. Previous employee of Roche, makers of tocilizumab (anti IL6 antibody) and CMO of Novimmune, makers of empalumab (anti IFN gamma antibody).”

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