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No link between flu vaccination in utero and child health problems
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There are no links between exposure to the 2009 pandemic H1N1 influenza vaccine during pregnancy and early childhood health problems, according to a recent study published in The BMJ.
“Our findings mean that health care providers can feel confident when recommending influenza vaccination to pregnant women,” Laura Walsh, MS, a data analyst at BORN Ontario and the study’s lead author, told Infectious Diseases in Children. “The results add to the already strong safety profile of flu shots during pregnancy and should help ease concerns by showing no negative health effects for children’s first 5 years of life.”
The study followed 104,249 Canadian children born from November 2009 through October 2010 until 5 years of age. According to the researchers, 30% of the population was exposed to the pH1N1 influenza vaccine in utero. They found no significant associations between vaccination and “upper or lower respiratory infections, otitis media, any infectious diseases, neoplasms, sensory disorders, urgent and inpatient health services use, pediatric complex chronic conditions, or mortality.”
A weak connection was discovered between in utero pH1N1 influenza vaccine exposure and a decreased risk for gastrointestinal infections (adjusted incidence rate ratio = 0.94; 95% CI, 0.91-0.98) and an increased risk for asthma (adjusted HR = 1.05; 95% CI, 1.02-1.09), but researchers believe these results can be attributed to residual confounding.
The study’s findings echo other reports that found no correlation between influenza vaccinations in pregnant mothers and health issues in their children, including a 2017 study that observed “no new or unexpected patterns in fetal or maternal outcomes” from 2010 to 2016.
“A large body of evidence supports the safety of influenza vaccination during pregnancy on newborn health, and this large population-based study extends this assessment to the child’s first 5 years of life,” Walsh said. “Further research is necessary to replicate these findings in different populations and with different influenza vaccines.” – by Eamon Dreisbach
References:
Moro P, et al. Drug Saf. 2017;doi:10.1007/s40264-016-0482-1.
Walsh LK, et al. BMJ. 2019;doi:10.1136/bmj.l4151.
Disclosures: Walsh reports no relevant financial disclosures. Please see the study for all other authors’ relevant financial disclosures.
Perspective
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Bernhard L. “Bud” Wiedermann, MD, MA
A group of Canadian investigators performed a retrospective cohort study looking at 5-year outcomes of children born to mothers in 2009-2010 who received the 2009 H1N1 flu vaccine, compared with infants whose mothers were not vaccinated during pregnancy. The study focused on 31,295 infants of mothers who received the vaccine compared with over 70,000 children without maternal vaccine exposure. The investigators looked at a variety of outcomes available in administrative databases, including a variety of infections, asthma, vision and hearing problems, cancer, complex chronic conditions and mortality.
One of the main problems with this type of study is that unexplained confounding factors can alter results. For example, mothers who chose to receive flu vaccine also might tend to seek medical care more frequently for their children, and that behavior might result in their children receiving more diagnoses of infections or asthma compared with children of mothers who do not seek health care as frequently. This could result in bias for adverse outcomes of maternal vaccine exposure. Researchers used an appropriate method — propensity scoring — to minimize bias in the analysis.
The researchers found no association of maternal flu vaccination with most of the outcomes of interest. They did find a small increase in rates of pediatric asthma in the vaccinated cohort, but this disappeared with further sensitivity analyses. The only statistically significant finding that persisted was a very small lower rate of gastrointestinal infections in the children whose mothers were immunized during pregnancy. This association, even if it was truly linked to maternal flu vaccine, was so small that it is unlikely to be clinically important.
Overall, this study should provide great reassurance to mothers who fear harmful effects for their infants from maternal flu vaccination during pregnancy. Further prospective studies may help define whether any benefits, such as protection from GI infections, accrue in these infants.
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