Flu vaccine during pregnancy does not harm children’s health years later

Influenza vaccines given to pregnant women do not pose an increased risk of adverse health effects in young children, Canadian researchers found in a retrospective cohort study.

Pregnant mothers who received a flu shot had offspring born without an increased risk of developing immune system related findings, such as asthma, or unrelated immune system findings, such as sensory impairment, over the course of of their early 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 use, the authors wrote in JAMA.

“In North America and many other countries around the world, although we advise all pregnant women to get the flu shot every year, many don’t,” said Fell. MedPage today. “So our motivation was really to try to generate high quality evidence that could contribute to our broader understanding of the long term safety of influenza vaccination during pregnancy.”

Fell added that other research has shown that one of the main reasons many pregnant women do not get the flu shot is “their safety concerns.” The authors cited previous studies that found associations between maternal vaccination during the H1N1 influenza pandemic in 2009 and premature births, as well as an increased risk of fetal death.

“Recognizing the safety concerns of mothers considering parenteral injection during pregnancy with empathy is essential. The evidence on benefit and safety, now including longer term outcomes in the offspring, is compelling,” Manish Patel, MD , CDC, and co-authors said in a accompanying editorial.

Fell and colleagues sought to provide evidence for the safety of maternal influenza vaccinations by finding out the effects on fetuses born after mothers were vaccinated and their health outcomes over the years to combat the reluctance to vaccinate against influenza.

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 an average follow-up of 3.6 years. Babies in the study had to weigh at least 500 grams and be born after at least 20 weeks gestation.

The primary outcomes of this population-based study included outcomes related to the immune system (such as infections or asthma) and outcomes not related to the immune system (such as sensory disturbances or neoplasms. ). Other outcomes were nonspecific outcomes, such as inpatient healthcare utilization, emergency room visits, or emergency hospitalization. A negative control was used to combat study biases, which included unvaccinated pregnant mothers and their offspring.

There were 28,255 children included in this study. Of these, 49% were girls and almost all were born at 37 weeks gestation or more. There were 36.2% of children born to mothers who received the seasonal flu vaccine during pregnancy. Mothers who received the flu shot were more likely to be 35 or older and have a pre-existing medical condition, and less likely to be current or former smokers or to live in low-income neighborhoods.

There was no significant association 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, CI to 95% 0.94-1.59) or the development of neoplasms (incidence rate 0.32 versus 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 1000 person-years; aHR 0.82, 95% CI 0.49- 1.37).

After adjustment, there was no association between maternal influenza vaccinations and the development of infections in infancy (incidence rate 184.6 vs. 179.1 per 1,000 person-years; ratio of adjusted incidence rates [aIRR] 1.07, 95% CI 0.99-1.15).

“We evaluated various health outcomes in children including pediatric health outcomes related to the immune system such as rates of asthma, ear infections, respiratory infections and other infections and found no association with influenza vaccination during pregnancy, ”said Fell. “I wouldn’t say it was surprising, but it was very reassuring.”

In addition, there was no association between the influenza vaccine and the use of emergency or inpatient care services (incidence rate of 511.7 versus 477.8 per 1,000 person-years. ; TRAI 1.05, 95% CI 0.99-1.16).

“The rates of adverse outcomes were similar between vaccinated and unvaccinated mothers,” the columnists wrote. “Efforts are needed now to encourage maternal influenza vaccination worldwide and to act on the convincing evidence of efficacy and safety.”

Fell and his colleagues noted the limitations of the study, including possible misclassified results due to a lack of validation of the results. Outcome parameters were limited to emergency visits and hospitalizations only, which excluded less serious unreported outcomes.