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expert reaction to a study looking at mRNA Covid-19 vaccine safety in pregnant women

A study published in the New England Journal of Medicine (NEJM) looks at mRNA Covid-19 Vaccine Safety in Pregnancy.


Dr Allyah Abbas-Hanif, Member of the Paediatrics and Pregnancy Expert Group of the Faculty of Pharmaceutical Medicine, said:

“The COVID-19 pandemic has disproportionately affected pregnant women and their infants.

“Pregnant women with COVID-19 have a 76% increased risk of preeclampsia and soberingly, maternal deaths associated with COVID-19 have been noted to be 22 times higher than those in non-infected pregnant women [1]. Treatments and prophylactic measures are therefore very much warranted. Many countries have prioritised pregnant women for vaccination but this is on the basis of developmental and reproductive toxicology studies conducted in animals and a positive risk benefit profile in women of child-bearing age. Pregnant women were however, actively excluded from the large phase 3 clinical trials. This study gives us a coarse but welcome update from the US based V-safe Surveillance System and Pregnancy Registry. This is an actively enrolling CDC smartphone app, which asks users to voluntarily undertake online surveys and telephone interviews to assess for side effects. Analysis is then made against pre-COVID population rates for pregnancy and neonatal outcomes.

“The update reveals women in the US are choosing to have vaccines across the gestational period. In 827 pregnant women who had completed pregnancies and received one or two doses of mRNA vaccines (Pfizer or Moderna), the study reports no increased rates of miscarriage and still births, compared to pre-COVID background rates. There were no increases in preterm labour or negative effects on newborns, including congenital abnormalities. Although this study provides no worrying safety signals, it is riddled with limitations. The methodology is not specific to pregnancy alone, there is no matching to controls, there is misclassification, recall bias and a large proportion of the cohort were health care professionals who are more likely to engage with health and pharmacovigilance studies.

“Despite these limitations, this update builds on the data clinicians, patients and governments need to make critical decisions to support pregnant women through this pandemic. High quality data is now needed to categorically understand unanswered clinical questions, such as the optimum window for offering gestational COVID-19 vaccines and how long immunity lasts (with ever-worrying variants on the horizon). The post-marketing BNT162b2 phase 2/3 study and hopefully others like it will be critical.

“Having said this, there needs to be an urgent shift in maternal research policy and investment. Regulators and sponsors must afford pregnant women the same timely access to drug development plans and research, so clinical questions can be answered promptly and robustly.”

  1. Villar, J., et al., Maternal and Neonatal Morbidity and Mortality Among Pregnant Women With and Without COVID-19 Infection: The INTERCOVID Multinational Cohort Study. JAMA Pediatr, 2021.



‘Preliminary Findings of mRNA Covid-19 Vaccine Safety in Pregnant Persons’ by Shimabukuro  et al was published in the New England Journal of Medicine on Thursday 17th June.

DOI: 10.1056/NEJMoa2104983



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