COVID vaccines safe for mums-to-be and prevent COVID dangers in pregnancy

COVID vaccines are safe for both pregnant women and those planning a pregnancy, two large studies of population-wide health data from England and Wales have shown.

Vaccination reduces risk of premature birth, having a smaller-than-average baby and pregnancy-related health problems like high blood pressure. Pregnant women and those planning a pregnancy should therefore be a priority group for vaccination in future pandemics, the study authors say, following the research enabled by the BHF Data Science Centre at Health Data Research UK.

“These are seminal studies of looking at whole population cohorts of pregnant women – a huge achievement. Our findings have shown that vaccination is safe for women of reproductive age before they get pregnant, but also during pregnancy,” says the University of Bristol’s Dr Rachel Denholm, a co-author on both studies.

The risks of COVID-19 in pregnancy are well known and the World Health Organization recommends that all pregnant women should be vaccinated. Despite this, a quarter of women of reproductive age in England and Wales remain unvaccinated, particularly younger and ethnic minority women. This wariness could partly be down to the lack of direct evidence to guide women’s decisions around vaccination, which these studies set out to address.

“Pregnant women were not prioritised at the beginning of the COVID-19 vaccination programme because there were concerns about safety. This probably has reduced participation of pregnant women during the first rounds of vaccination because they were afraid, and vaccination in this group has remained low,” says lead author of the second study, Dr Elena Raffetti from the BHF Cardiovascular Epidemiology Unit in Cambridge.

“Pregnant women should be considered a priority vaccination group in future pandemics and they can be reassured about vaccination safety,” she adds.

The two studies involved health record data from the entire population of England (as well as Wales in the second study) where all personal identifying information has been removed. The findings show that:

• Vaccination with the mRNA (Pfizer) vaccine is safe in pregnant women; no negative side effects were found in vaccinated people when compared with unvaccinated.
• Pregnant women infected with COVID-19 have a higher risk of both common pregnancy-related health problems such as high blood pressure, premature birth and smaller than average babies.
• Infection during pregnancy is also linked with a higher risk of stillbirth, although this effect was only seen within 14 days of a positive COVID test or if a woman became infected during the third trimester of her pregnancy.
• COVID jabs lower the risk of several pregnancy-related health problems for both expectant mums and their babies, including high blood pressure, premature birth and smaller babies, compared with women who were not vaccinated.
• Vaccination up to 12 months before pregnancy is also safe and lowers these health risks.
• The mRNA vaccine (the Pfizer jab) is safer for pregnant women than the traditional viral-vector vaccine (the Oxford-AstraZeneca jab). Findings showed a very small increased risk of stillbirth and dangerous blood clots compared with the Pfizer vaccine, however this is a considerably lower risk than that posed by COVID infection itself, and of a similar level to the risks of taking hormone replacement therapy or the contraceptive pill, the authors say.

The first of the two studies, both published in the Lancet, investigated whether getting vaccinated in the 12 months up to becoming pregnant and including the first 24 weeks of pregnancy had any impact on the health of expectant mothers and their babies. It included all pregnancies in England between May 2021 and October 2022, using linked electronic health records from 186,990 women.

Lead author Dr Luisa Zuccolo, from Human Technopole in Milan, explains: “The clear message from our results is that it is by far safer to start a pregnancy as vaccinated against COVID-19, rather than unvaccinated. We confirm that the decision to vaccinate women of reproductive age was indeed the best course of action as it prevented adverse pregnancy and birth outcomes in thousands of mothers and children in the UK and elsewhere.”

The second study involved the whole population of England and Wales; the largest of its kind to date, and the first to study a wide range of common and rare health problems in pregnancy after both COVID-19 infection and vaccination. It used linked electronic health records of 865,654 pregnant women who were infected with COVID-19 during the first wave of the pandemic and the subsequent vaccination periods (from August 2019 to December 2021). It is unique in looking at the effect of COVID-19 on pregnancy complications over each trimester, and according to the virus variants that were prevalent at different times.

Lead author Dr Raffetti says: “Our study confirms that COVID infection increased risk of gestational hypertension, preeclampsia, gestational diabetes and preterm birth. There were conflicting results before the study on stillbirth, and in our research we saw that stillbirth was increased only in the first two weeks after COVID infection. This might also be a reverse causality [ie stillbirth increasing risk of catching COVID rather than the other way around] or a very short-term effect of COVID infection.”

“Also vaccinated women had reduced adverse pregnancy outcomes, because they probably had a lower risk of getting COVID, so there was a very significantly lower level of preterm birth in this group of women.”

Both research teams used de-identified hospital data on births to pinpoint pregnancies and linked them to the vast amounts of data available in the CVD COVID UK consortium on COVID-19 vaccination and infection, routinely collected GP records, and medications mortality data.