Study: Safety of COVID-19 vaccines in pregnancy: Canadian National Network of Vaccine Safety (CANVAS) cohort study. Image credit: MM Vieira/Shutterstock
Record
Several observational studies have described adverse event rates after the first and second doses or booster doses of messenger ribonucleic acid (mRNA)-based COVID-19 vaccines in pregnancy. Most studies included only one cohort of pregnant women and documented all adverse health events with limited differentiation of major/severe/severe adverse events. Clearly, most studies lacked a contemporary pregnant, unvaccinated control group.
About the study
In the present study conducted as part of the Canadian National Vaccine Safety (CANVAS) network, researchers monitored the safety of the COVID-19 vaccine in pregnant women in seven Canadian provinces representing more than 75% of the national population. Eligible vaccinated and non-pregnant women had received their first dose of COVID-19 vaccine within the past seven days. They also had an active email address and phone number and communicated in English or French. In addition, they were residents of any of these seven Canadian provinces, namely Ontario, Quebec, British Columbia, Alberta, Nova Scotia, Yukon, and Prince Edward Island. The researchers compared the rates of health events in vaccinated pregnant women and vaccinated non-pregnant women of the same age (between 15 and 49 years). The control group included unvaccinated pregnant women and vaccinated non-pregnant subjects. The study assessed all health events, including new or worsening health events after vaccination in the previous seven days for controls and in the seven days after vaccination in those who received a COVID-19 vaccine. First, the researchers calculated the rates of major and serious health events, including all symptoms, after the first and second vaccinations. To examine associations between outcomes and exposures, they constructed univariate and multivariate logistic regression models for each exposure type, as follows: i) vaccination status among pregnant women and ii) pregnancy status in vaccinated individuals. They restricted the statistical modeling to those who received either of these two mRNA vaccines, BNT162b2 and mRNA-1273. They reported an odds ratio (OR) with 95% confidence intervals (CI). In the first sensitivity analyses, the primary endpoint, a major health event after vaccination, was restricted to new or worsening health events resulting in medical consultation in the previous seven days. The researchers repeated the same analysis after the first and second vaccinations. In the second sensitivity analysis, they restricted the data set to those pregnant women who were in excellent health and compared the results from the original analysis.
Study findings
By November 4, 2021, 1,91,360 and 94,937 women aged 15 to 49 years and of known pregnancy status had completed the first and second vaccine dose surveys, respectively. Of these, 226 of 5597 vaccinated pregnant women experienced a major health event after the first dose and 227 of 3108 after the second dose of an mRNA vaccine. Among the controls, only 11 of 339 pregnant unvaccinated women experienced a major health event after vaccination. Pregnant vaccinated women had increased odds of a major health event within seven days of vaccine after dose two of mRNA-1273 (adjusted OR 4.4 [95% CI]) compared to pregnant unvaccinated controls in the last seven days. One dose of mRNA-1273 or one or two doses of the BNT162b2 vaccine did not increase the odds of major health events among study participants. Specifically, the researchers assessed those health events that affected work, school, or required medical attention. The authors observed events requiring medical attention remained similar in all analyses. Pregnant vaccinated women had reduced odds of a major health event compared with non-pregnant vaccinated women after the first dose (aOR 0.63) and second dose (aOR 0.62) of any mRNA vaccination.
conclusions
Overall, both of the COVID-19 mRNA vaccines evaluated in the study were shown to be safe for pregnant women. They had significantly lower rates of adverse health events after vaccination than non-pregnant vaccine recipients of both mRNA vaccines used in Canada. after one and two doses. However, overall rates of post-vaccination adverse health events were higher after dosing two of the mRNA-1273 vaccine recipients. Since COVID-19 causes significant complications in pregnancy, it is important to provide higher vaccine coverage to pregnant women. In the future, data from the current study could inform pregnant women about the reactivity of COVID-19 vaccines during pregnancy. In addition to vaccine efficacy and immunogenicity data, these data could help clinicians recommend the best use of COVID-19 vaccines in pregnancy.
