according to Laura K. Walsh of the University of Ottawa and associates.
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The investigators conducted a population-based retrospective cohort study from November 2009 to October 2010 of all live births within the province of Ontario. Of the 104,249 eligible live births reported to the Ontario birth registry, 31,295 were exposed to the H1N1 vaccine in utero. After adjustment, there were no significant differences in the women who did and did not receive vaccines during pregnancy, according to the study, published in the BMJ.
After a median follow-up of 5 years, 14% of children received an asthma diagnosis, with a median age at diagnosis of 1.8 years. Children were more likely to receive an asthma diagnosis if their mothers had a preexisting condition or if they were born preterm. At follow-up, 34% of children had at least one upper respiratory tract infection. Sensory disorder, neoplasm, and pediatric complex chronic condition were rare, each occurring in less than 1% of the study cohort (BMJ. 2019 Jul 10. doi: 10.1136/bmj.l4151).
No significant association was found between prenatal exposure to the H1N1 vaccine and upper or lower respiratory infections, otitis media, all infections, neoplasms, sensory disorders, rates of urgent and inpatient health services use, pediatric complex chronic conditions, or mortality. A weak but significant association was observed for asthma (adjusted hazard ratio, 1.05; 95% confidence interval, 1.02-1.09), and a weak inverse association was found for gastrointestinal infections (adjusted incidence rate ratio, 0.94; 95% CI, 0.91-0.98).
“Although we observed a small, but statistically significant, increase in pediatric asthma and a reduction in gastrointestinal infections, we are not aware of any biologic mechanisms to explain these findings. Future studies in different settings and with different influenza vaccine formulations will be important for developing the evidence base on longer-term pediatric outcomes following influenza vaccination during pregnancy,” the investigators concluded.
The study was funded by grants from the Canadian Institutes of Health Research and the Institute for Clinical Evaluative Sciences.