In a recent study published in The Lancet Infectious Diseases, researchers investigated the incidence of significant health events among pregnant women after vaccination against coronavirus 2019 (COVID-19) in seven Canadian provinces between November 1 of 2021 and May 9, 2022.
Study: Safety of COVID-19 vaccines in pregnancy: a Canadian national safety network cohort study (CANVAS). Image credit: MM Vieira/Shutterstock
background
Several observational studies have described adverse event rates after the first and second dose or booster doses of messenger ribonucleic acid (mRNA)-based COVID-19 vaccines during pregnancy. Most studies included only one cohort of pregnant women and documented all adverse health events with limited differentiation of significant/severe/serious adverse events. Clearly, most studies did not have a contemporary, pregnant, unvaccinated control group.
About the study
In the present study conducted under the Canadian National Vaccine Safety (CANVAS) network, researchers monitored the safety of the COVID-19 vaccine in pregnant women from seven Canadian provinces representing more than 75% of the national population.
Eligible vaccinated and non-vaccinated pregnant and non-pregnant women had received the first dose of a COVID-19 vaccine within the past seven days. In addition, they 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 (15 to 49 years). The control group consisted of non-vaccinated pregnant women and vaccinated non-pregnant individuals.
The study assessed all health events, including health events that were new or worsened after vaccination in the previous seven days for controls and the seven days after vaccination in those who received a measles vaccine. COVID-19. First, the researchers estimated the rates of significant and serious health events, including all symptoms, after the first and second vaccinations. To examine associations between outcomes and exposures, they constructed univariable and multivariable logistic regression models for each type of exposure, as follows:
i) vaccination status of pregnant women, i
ii) pregnancy status among vaccinated persons.
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, ie a significant 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 of the primary analysis.
Results of the study
As of November 4, 2021, 1,91,360 and 94,937 women aged 15–49 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 significant health event after dose 1 and 227 of 3108 after dose two of an mRNA vaccine. Among controls, only 11 of 339 unvaccinated pregnant women experienced a significant health event after vaccination.
Vaccinated pregnant women had increased odds of a significant health event within seven days postvaccine after dose two of mRNA-1273 (adjusted OR of 4.4 [95% CI]) compared to pregnant controls not vaccinated during the last seven days. One dose of mRNA-1273 or one or two doses of the BNT162b2 vaccine did not increase the odds of significant health events among study participants.
Specifically, the researchers assessed those health events that affected work, schooling, or required medical attention. The authors observed events requiring medical attention remained similar in all analyses. Pregnant vaccinated women had decreased odds of a significant health event compared with nonpregnant vaccinated women after dose 1 (aOR 0.63) and dose two (aOR 0.62) of any mRNA vaccine.
Conclusions
Overall, the two COVID-19 mRNA vaccines evaluated in the study were found to be safe for pregnant women. They had significantly lower rates of adverse health events after vaccination than non-pregnant vaccine recipients of the two mRNA vaccines used in Canada; after one and two doses. However, overall rates of adverse health events after vaccination were higher after dose two in mRNA-1273 vaccine recipients. Since COVID-19 causes significant complications during pregnancy, it is crucial to provide higher vaccine coverage to pregnant women.
In the future, the current study data could inform pregnant women about the reactogenicity 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 during pregnancy.