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expert reaction to preprint looking at COVID-19 infection (with the alpha or the delta variant) in hospitalised pregnant women, and their vaccination status

A preprint, an unpublished non-peer reviewed study, looks at impact of SARS-CoV-2 variant on the severity of maternal infection and perinatal outcomes.


Dr Edward Mullins, NIHR Academic Clinical Lecturer, Imperial College London, said:

“These robust data will be invaluable to support campaigns to increase the number of women in (or considering) pregnancy taking-up vaccination against SARS-CoV-2 as soon as possible.  This will prevent serious illness, increased with new variants, and pre-term birth.

“It will be crucial to encourage women in pregnancy to take part in the trials of available SARS-CoV-2 vaccines in pregnancy, underway in the UK, to gather further robust data on safety and immunity over time for mothers and babies.  These, with real-world data on safety from over 200,000 women in the USA, will give women in pregnancy the information they need for peace of mind when choosing vaccination.”


Prof Andrew Shennan, Professor of Obstetrics, King’s College London, said:

“This is an important study, prospectively collected by an established national obstetric surveillance system and therefore very reliable.  Compared to the original covid virus the new variants (alpha and then delta) caused progressively more severe disease in pregnant women.  This included need for ventilation, intensive care admission and pneumonia, more than 50% more likely to occur.  The authors considered other reasons why covid may have appeared worse later on, such as admission thresholds being lower and more frequent testing; they also controlled for other medical conditions and social factors.  However they concluded the symptomatic women included in the study would have been treated the same, and the later variants were therefore worse.

“No vaccinated woman was admitted to hospital and this stresses the importance of vaccination, even in pregnancy.  There are no known additional risks of vaccination in pregnancy and it is now routinely recommended.  It is likely these variants are more severe in all populations, as these findings  have only been exposed by this unique collection of data that only includes pregnant women.  Worldwide vaccination is required to stop these new variants emerging.”



Preprint (not a paper): ‘Impact of SARS-CoV-2 variant on the severity of maternal infection and perinatal outcomes: Data from the UK Obstetric Surveillance System national cohort’ by Nicola Vousden et al.  This work is not peer-reviewed.



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



Declared interests

Prof Andrew Shennan: “No conflicts.”

None others received.

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