Influenza vaccines given to pregnant mothers do not result in any increased risk of adverse health outcomes for young children, Canadian researchers found in a retrospective cohort study.
Pregnant mothers who received an influenza vaccine had offspring born without any greater risk of developing immune-related outcomes, such as asthma, or non-immune-related outcomes, such as sensory impairment, during their first few years of life, reported Deshayne B. Fell, PhD, of the Children’s Hospital of Eastern Ontario Research Institute in Ottawa, and colleagues.
These vaccines were also not significantly associated with infections, neoplasms, or healthcare utilization, the authors wrote in JAMA.
“In North America and many other countries internationally, although we advise all pregnant women to receive a flu shot each year, many do not,” Fell told MedPage Today. “So our motivation was really about trying to generate high quality evidence that could contribute to our broader understanding about long-term safety of influenza vaccination during pregnancy.”
Fell added that other research has shown that a leading reason why many pregnant people do not get the flu shot is “due to their concerns about safety.” The authors cited prior studies that found associations between maternal vaccination during the H1N1 flu pandemic in 2009 and preterm births, as well as an increased risk for fetal death.
“Acknowledging the safety concerns of mothers considering a parenteral injection during pregnancy with empathy is essential. Data on the benefits and safety, now including longer-term outcomes in offspring, are compelling,” Manish Patel, MD, of the CDC, and co-authors stated in an accompanying editorial.
Fell and colleagues sought to provide evidence for the safety of maternal influenza vaccinations by discovering the effects on fetuses born after mothers received vaccinations and their health outcomes as the years progressed to combat influenza vaccine hesitancy.
Health data was obtained from a birth registry to include all live births from October 1, 2010 to March 31, 2014 in Nova Scotia, Canada. Follow-up ended after March 31, 2016 with a mean follow-up of 3.6 years. Babies in the study had to weigh at least 500 grams and be born after at least 20 gestational weeks.
The main outcomes of this population-based study included immune-related outcomes (such as infections or asthma) and non-immune-related outcomes (such as sensory impairments or neoplasms). Other outcomes were non-specific outcomes, such as inpatient healthcare utilization, emergency visits, or urgent hospitalization. A negative control was used to combat study bias, which included unvaccinated pregnant mothers and their offspring.
There were 28,255 children included in this study. Of these, 49% were girls and nearly all were born at 37 weeks or more gestation. There were 36.2% of children born to mothers who received the seasonal influenza vaccine during pregnancy. Mothers who had the flu shot were more likely to be 35 years or older and to have a preexisting medical condition, and less likely to be current or former smokers or reside in lower income neighborhoods.
There was no significant link between maternal influenza vaccination and the development of childhood asthma (incidence rate 3.0 vs 2.5 per 1,000 person-years; adjusted HR 1.22, 95% CI 0.94-1.59) or development of neoplasms (incidence rate 0.32 vs 0.26 per 1,000 person-years; aHR 1.26, 95% CI 0.57-2.78). Maternal influenza vaccinations were also not associated with sensory impairment (incidence rate 0.80 vs 0.97 per 1,000 person-years; aHR 0.82, 95% CI 0.49-1.37).
After adjustment, there was no link between maternal influenza vaccinations and the development of infections during early childhood (incidence rate 184.6 vs 179.1 per 1,000 person-years; adjusted incidence rate ratio [aIRR] 1.07, 95% CI 0.99-1.15).
“We assessed various health outcomes in the children, including immune-related pediatric health outcomes such as rates of asthma, ear infections, respiratory infections, and other infections and did not find any association with influenza vaccination during pregnancy,” Fell said. “I wouldn’t say that this was surprising, but it was very reassuring.”
In addition, there was no association between influenza vaccine and the use of urgent or inpatient healthcare services (incidence rate 511.7 vs 477.8 per 1,000 person-years; aIRR 1.05, 95% CI 0.99-1.16).
“The rates of adverse outcomes were similar between vaccinated and unvaccinated mothers,” the editorialists wrote. “Efforts are needed now to encourage maternal influenza vaccination worldwide and to act on the compelling efficacy and safety data.”
Fell and colleagues noted study limitations, including possible misclassified outcomes due to a lack of outcome validation. Outcome parameters were limited to only emergency visits and hospitalizations, which excluded less severe unreported findings.
Zaina Hamza is a staff writer for MedPage Today, covering Gastroenterology and Infectious disease. She is based in Chicago.
Unrelated to this study, Benchimol received legal consulting fees from the company Hoffmann La-Roche Limited. Top received consulting fees from Pfizer in addition to grants from GlaxoSmithKline. Ortiz received consultancy fees from Seqirus, Foundation for Influenza, Pfizer, in addition to research support from the NIH, GlaxoSmithKline, and Pfizer. Another coauthor reported serving as the CEO of CANImmunize Inc. No additional conflicts of interest were reported. Grant funding was provided by the Canadian Institutes of Health Research.