Vaccines against Covid-19 that use messenger RNA (mRNA), such as that of Pfizer and Moderna, are safe for use in pregnancy. Pregnant women had lower rates of adverse events after vaccination than nonpregnant, age-matched immunized people.
The data are from a wide canadian study published in the scientific journal “Lancet Infectious Diseases” this Thursday (11). Scientists performed the analysis of vaccine side effects in immunized pregnant women and compared it with two other groups: unvaccinated pregnant women and immunized women who were not pregnant.
“In the early stages of the Covid-19 vaccine launch, there was low uptake of the vaccine among pregnant women due to concerns about data availability and safety. There is still below-average absorption among non-pregnant women of childbearing age,” says scientist Manish Sadarangani, from the Children’s Hospital Research Institute of British Columbia, Canada.
According to the expert, the observational study provides in-depth information on the rates of adverse health events in pregnant women after different vaccination schedules against the disease. “This information should be used to inform pregnant women about side effects that may occur in the week following vaccination,” Sadarangani says.
Study highlights
Conducted by Canada’s National Vaccine Safety Network (Canvas), the study analyzed data from participants in seven Canadian provinces and territories between December 2020 and November 2021.
All vaccinated volunteers were asked to report any health events during the seven days following each dose of coronavirus vaccine. The group of unimmunized pregnant women, technically called the “control”, was asked to record any clinical problems in the seven days prior to completing the survey.
In total, 191,360 women aged 15 to 49 with known pregnancy status completed the first dose survey and 94,937 completed the second dose survey.
In the study, a “significant health event” was defined as a new or worse health situation that was sufficient to cause the participant to miss school or work, require a medical appointment, or prevent daily activities for the previous seven days.
A “serious health event” was defined as any impact that resulted in an emergency department visit or hospitalization in the last seven days.
The researchers found that 4% of pregnant women vaccinated with mRNA immunizers, a total of 226 out of 5,597, reported a significant health event within seven days after the first dose of an mRNA vaccine. After the second dose, the rate rose to 7.3%, as 227 reports from a total of 3,108 volunteers.
According to the study, the most common significant health events after the second dose in pregnant women were a general feeling of being unwell, headache or migraine, and respiratory tract infection.
In comparison, 3.2% of unvaccinated pregnant participants reported similar events in the seven days prior to completing the survey.
In the control group, which includes vaccinated women who were not pregnant, 6.3% reported a significant health event in the week after the initial dose. In relation to the second dose, the rate was 11.3%.
The study points out that serious health events were rare in all groups (less than 1%) and occurred at similar rates in the three groups evaluated after dose one and dose two.
Miscarriage or fetal death after 20 weeks’ gestation was the most frequently reported adverse pregnancy outcome, with no significant difference between rates in vaccinated and unvaccinated women.
Data indicate that 2.1% of unvaccinated pregnant women and 1.5% of vaccinated pregnant women experienced miscarriage or stillbirth within seven days after the 1st dose of any mRNA vaccine.
“The lower rate of significant health events among vaccinated pregnant women compared to vaccinated non-pregnant women is unexpected and requires further research. Previous studies of other vaccines in pregnant women have mostly not reported significant differences in health events between pregnant and non-pregnant women or found higher rates in pregnancy,” says researcher Julie Bettinger, study author and a fellow at British Columbia. Children’s Hospital Research Institute.
Julie says that more studies of messenger RNA vaccines against other diseases are needed to identify whether the reduced side effects seen in pregnant women in the current study are a feature of the mRNA vaccine platform or these specific vaccines.
Research continuity
Among the limitations of the study, the authors point out that the majority of participants who reported ethnicity in this study were white. This suggests that the data may not be fully applicable to other populations.
In addition, the study focused on health events that occurred within the first seven days after vaccination. Long-term reactions were not evaluated in the research, which remains ongoing.
“These findings are consistent and add to the growing body of evidence that Covid-19 mRNA vaccines are safe during pregnancy. Vaccination against Covid-19 among pregnant women remains lower than among non-pregnant women of childbearing age,” said researchers Sascha Ellington and Christine Olson of the US Centers for Disease Control and Prevention (CDC).
“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 effectiveness of vaccination in pregnancy and encourage healthcare providers to promote immunization throughout all trimesters of pregnancy.” .
Source: CNN Brasil
