The COVID-19 pandemic has disproportionately affected pregnant women, who are at higher risk of severe COVID-19 disease compared to non-pregnant people of a similar age. Vaccines for COVID-19 have been recommended for use in pregnancy in many countries early in vaccine implementation, based on the established prior safety of inactivated vaccines in pregnancy and reassuring data from the small number of pregnancies that occurred during vaccine trials pre-approval. This study is one of the first to examine vaccine side effects in a group of vaccinated pregnant women simultaneously with a group of unvaccinated pregnant women and with a vaccinated non-pregnant group to allow comparison between the three.
In the early stages of the COVID-19 vaccine launch, there was low vaccine uptake among pregnant women due to concerns about data availability and vaccine safety. There is even lower than average uptake among non-pregnant women of reproductive age. Large observational studies such as ours are crucial to properly understand the rates of adverse health events in pregnant women after different doses of COVID-19 vaccination. This information should be used to inform pregnant women about the side effects they may experience in the week after vaccination.”
Dr. Manish Sadarangani from the British Columbia Hospital Children’s Research Institute and first author of the study
This new study, from the Canadian National Network for Vaccine Safety (CANVAS), looked at data from participants in seven Canadian provinces and territories between December 2020 and November 2021. All vaccinated participants were asked to self-report any health events during of seven days each dose of the COVID-19 vaccine. The unvaccinated control group of pregnant women were asked to record any health problems in the seven days before completing the survey. 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. A “major health event” was defined as a new or worsening health event that was sufficient to cause the participant to miss school/work, require medical advice, and/or prevent daily activities in the previous seven days. A “serious health event” was defined as any event that resulted in an emergency department visit and/or hospitalization in the previous seven days. The researchers found that 4.0% (226/5,597) of pregnant women vaccinated with mRNA reported a major health event within seven days after the first dose of an mRNA vaccine and 7.3% (227/3,108) after the second dose. The most common major health events after the second dose in pregnant women were a general feeling of being unwell, headache/migraine and respiratory tract infection. In comparison, 3.2% (11/339) of pregnant unvaccinated participants reported similar events in the seven days before survey completion. In the vaccinated non-pregnant control group, 6.3% (10,950/174,765) reported a major health event in the week after the first dose and 11.3% (10,254/91,131) after the second dose. Serious health events were rare in all groups (less than 1%) and occurred at similar rates in vaccinated pregnant subjects, vaccinated non-pregnant subjects and unvaccinated controls after dose one and two. Miscarriage/stillbirth was the most commonly reported adverse pregnancy outcome with no significant difference between rates in vaccinated and unvaccinated women. 2.1% (7/339) of unvaccinated pregnant women and 1.5% (83/5,597) of vaccinated pregnant women experienced miscarriage or stillbirth within seven days after the first dose of any mRNA vaccine. “The lower rate of major health events among vaccinated pregnant women compared to vaccinated non-pregnant individuals is unexpected and requires more research. Previous studies of other vaccines in pregnant women have mostly reported no significant differences in health events between pregnant and non-pregnant women or have found higher rates in pregnancy.Further studies of non-COVID-19 mRNA vaccines are needed to determine whether the reduced adverse events seen in pregnant women in this study are a feature of the mRNA vaccine platform or of these specific vaccines.” says Dr. Julie Bettinger, senior author of this paper and also from the British Columbia Hospital Children’s Research Institute. The authors caution that most participants who reported ethnicity in this study were white, and thus these data may not be fully generalizable to other populations. Furthermore, this study focused on health events occurring within the first seven days after vaccination and therefore cannot draw any conclusions about long-term reactions. However, long-term follow-up of this cohort is ongoing. A further limitation of this study is that the data are based on self-reports by study participants, without verification by medical records. Writing in a linked commentary, Dr Sascha Ellington and Dr Christine Olson of the US Centers for Disease Control and Prevention (who were not involved in the study) note: “These findings are consistent and add to the growing body of evidence that mRNA vaccines of COVID-19 is safe during pregnancy. […] Vaccination against COVID-19 among pregnant women is still lower than among non-pregnant women of reproductive age. Given the risks of significant illness and adverse pregnancy outcomes, it is imperative that we continue to collect and disseminate data on the safety and efficacy of COVID-19 vaccination in pregnancy and encourage health care providers to promote vaccination in all the trimesters of pregnancy”. Source: Journal Reference: Sadarangani, M., et al. (2022) Safety of COVID-19 vaccines in pregnancy: a Canadian National Vaccine Safety Network (CANVAS) cohort study. Lancet Infectious Diseases. doi.org/10.1016/S1473-3099(22)00426-1.
