Covid-19 mRNA vaccines safe in pregnancy, study suggests

Study looked at vaccinated and unvaccinated pregnant women in Canada, as well as non-pregnant participants

A pregnant woman receives a vaccine for coronavirus at Skippack Pharmacy in Schwenksville, Pennsylvania, US. Reuters

Covid-19 mRNA vaccines are safe to use in pregnancy and pregnant women experience lower rates of health events post vaccination than similarly aged, non-pregnant vaccinated people, a study published in The Lancet Infectious Diseases journal reported.

Researchers found that the Covid-19 pandemic has disproportionately affected pregnant women, who are at a higher risk of severe Covid-19 compared with similarly aged non-pregnant people.

This study is one of the first to look at vaccine side effects in a group of vaccinated pregnant women, as well as unvaccinated pregnant women and a group of vaccinated non-pregnant people to enable comparisons between the three.

“In the early stages of the Covid-19 vaccine roll-out, there was low vaccine uptake among pregnant people due to concerns about data availability and vaccine safety,” said Dr Manish Sadarangani from the British Columbia Children's Hospital Research Institute and the first author on this study.

“There still is lower-than-average uptake among non-pregnant women of reproductive age.”

Information from the study will be used to inform pregnant women about the side effects they may experience in the week following vaccination, he added.

This study, from the Canadian National Vaccine Safety (Canvas) Network, looked at data from participants across seven Canadian provinces and territories between December 2020 and November 2021.

All vaccinated participants were asked to self-report any health events during the seven days following each dose of Covid-19 vaccine as part of the study. The unvaccinated pregnant group was asked to record any health problems over the seven days before they filled out the survey.

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In total, 191,360 women aged 15-49 years with known pregnancy status completed the first-dose survey and 94,937 completed the second-dose survey.

Researchers defined a “significant health event” as a new or worse health event that was enough to cause the participant to miss school or work, require medical consultation and/or prevent daily activities.

A “serious health event” was defined as any event resulting in an emergency department visit and/or admission to hospital.

The researchers found that 4 per cent of mRNA-vaccinated pregnant women reported a significant health event within seven days after dose one of an mRNA vaccine, and 7.3 per cent after dose two.

The most common significant health events after dose two in pregnant women were a general feeling of being unwell, headache or migraine and respiratory tract infection.

In comparison, 3.2 per cent of pregnant unvaccinated participants reported similar events in the seven days before survey completion.

In the vaccinated non-pregnant control group, 6.3 per cent of participants reported a significant health event in the week after dose one and 11.3 per cent after dose two.

Inside a Covid-19 ward at King's College Hospital in London — video

Serious health events were rare in all groups — fewer than 1 per cent — and occurred at similar rates in vaccinated pregnant people, vaccinated non-pregnant people and unvaccinated participants after dose one and dose two.

Miscarriage and stillbirth were the most frequently reported adverse pregnancy outcomes, with no significant difference between the rates in vaccinated and unvaccinated women.

From the unvaccinated pregnant women group, 2.1 per cent and 1.5 per cent of vaccinated pregnant women experienced a miscarriage or stillbirth within seven days after dose one of any mRNA vaccine.

“The lower rate of significant health events amongst vaccinated pregnant people, compared with vaccinated non-pregnant individuals, is unexpected and requires more research,” said Dr Julie Bettinger, also from the British Columbia Children’s Hospital Research Institute and senior author on the paper.

“Further studies of non-Covid-19 mRNA vaccines are required to identify if the reduced side effects observed in pregnant people in this study is a feature of the mRNA vaccine platform or of these specific vaccines.”

The authors caution that most participants who reported ethnicity in this study were white and the data may therefore not be fully generalisable to other populations.

In addition, the study focused on health events occurring within the first seven days following vaccination and so cannot conclude anything about longer-term reactions. However, longer-term follow-up of this cohort is ongoing.

A further limitation of this study is that data are based on self-reports from study participants, without verification by medical records.

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“These findings are consistent with and add to the growing body of evidence that Covid-19 mRNA vaccines are safe during pregnancy,” said Dr Sascha Ellington and Dr Christine Olson from the Centres for Disease Control and Prevention in the US, who were not involved in the project.

“Covid-19 vaccination among pregnant people continues to be lower than among non-pregnant females of reproductive age.”

They went on to note that given the risks of significant illness and adverse pregnancy outcomes, it is imperative that medical professionals continue to collect and disseminate data on the safety and effectiveness of Covid-19 vaccination in pregnancy.

It was also noted that it is important to encourage healthcare providers to promote vaccination during all trimesters of pregnancy.