mRNA vaccines safe for use in pregnant woman, confirms large-scale study

COVID-19 mRNA vaccines are safe to use during pregnancy with pregnant women experiencing lower rates of health events post-vaccination than non-pregnant vaccinated people of the same age, according to a large-scale Canadian study published in The Lancet Infectious Diseases journal.

The Covid-19 pandemic has disproportionately affected pregnant women, who are at higher risk of severe infection compared with non-pregnant individuals of similar age.

According to the report, the study is one of the first to look at vaccine side effects in a group of vaccinated pregnant women at the same time as both an unvaccinated pregnant group and a vaccinated non-pregnant group to enable comparisons between the three.

“In the early stages of the Covid-19 vaccine rollout, there was low vaccine uptake among pregnant people due to concerns about data availability and safety. There still is lower than average uptake among non-pregnant women of reproductive age,” says Dr Manish Sadarangani from the British Columbia Children’s Hospital Research Institute and the first author on this study in the report.

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

A “significant health event” was defined as a new or worse health event, which was enough to cause the participant to miss school/work, require medical consultation and/or prevent daily activities in the previous seven days. “Serious health event” was defined as any event resulting in an emergency department visit and/or hospitalisation in the previous seven days.

The researchers found that 4.0 per cent (226 out of 5,597) of mRNA-vaccinated pregnant females reported a significant health event within seven days after dose one of the shot and 7.3 per cent (227/3,108) after dose two. The most common significant health events after dose two in pregnant females were a general feeling of being unwell, headache/migraine, and respiratory tract infection.

In comparison, 3.2 per cent of pregnant unvaccinated participants reported similar events in the seven days prior to survey completion. In the vaccinated non-pregnant control group, 6.3 per cent reported a significant health event in the week after dose one and 11.3 per cent after dose two. Serious health events were rare in all groups (fewer than 1 per cent) and occurred at similar rates in vaccinated pregnant individuals, vaccinated non-pregnant people and unvaccinated controls after dose one and dose two.

Miscarriage/stillbirth was the most frequently reported adverse pregnancy outcome with no significant difference between the rates in vaccinated and unvaccinated women; 2.1 per cent of unvaccinated pregnant women 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 from the British Columbia Children’s Hospital Research Institute and senior author for the paper.

The authors caution that most participants who reported ethnicity in this study were white and these data may, therefore, can’t be fully generalised to other populations. Additionally, this study focused on health events occurring within the first seven days following vaccination and so, cannot conclude anything about reactions in the longer term.