Flu shot during pregnancy shows unexpected benefits in large study
May 22, 2012
Ottawa – Getting a flu shot during pregnancy provides unanticipated benefits to the baby, according to the authors of a large population-based study examining the issue. Specifically, the study showed that H1N1 vaccination during the pandemic was associated with a significantly reduced risk of stillbirth, preterm birth and extremely small babies at birth.
Researchers at the Ottawa Hospital Research Institute (OHRI), the CHEO Research Institute and the University of Ottawa (uOttawa) used data from Ontario's birth record database, BORN, to examine 55,570 single-child births that took place in Ontario during the H1N1 pandemic. The resulting paper, "H1N1 Influenza Vaccination during Pregnancy and Fetal and Neonatal Outcomes," was recently published by the American Journal of Public Health.
The study shows that, compared to pregnant women who were not immunized against H1N1, mothers who received the H1N1 vaccination were:
- 34% less likely to have a stillbirth,
- 28% less likely to deliver before 32 weeks, and
- 19% less likely to give birth to a child with a birth weight for gestational age in the bottom third percentile.
"These are all significant results, but especially interesting is the finding that the vaccinated mothers were one-third less likely to have a stillborn child," says lead author Deshayne Fell, an epidemiologist for BORN Ontario. "This is one of the only studies large enough to evaluate the association between maternal flu vaccination and stillbirth—a very rare event."
"What surprised me and the research team was the strength of the protective benefits we found," says co-author Dr. Ann Sprague, the Scientific Manager of BORN Ontario at the Children's Hospital of Eastern Ontario (CHEO) Research Institute.
The study also found no increase in adverse outcomes for H1N1-vaccinated mothers and their babies during the weeks before and just after birth, also referred to as the perinatal period.
"The findings of this study are very helpful," says co-author Dr. Mark Walker, a Senior Scientist at OHRI, a High-Risk Obstetrician at The Ottawa Hospital, and a Professor and Tier One Research Chair in Perinatal Research at the University of Ottawa.
"Pregnant women are generally very, very careful about what they put into their bodies. For health-care providers like me, such a large-scale study that shows no adverse perinatal outcomes resulting from the H1N1 flu vaccine will be extremely helpful when discussing maternal vaccination."
Of all the single-child births recorded from November 2009 to April 2010, 42% of the women received the H1N1 vaccination, which makes the findings robust. BORN—the Better Outcomes Registry & Network—collects data from all births in Ontario. In order to conduct the research for this study, questions about H1N1 vaccination were added to the database in advance of the H1N1 vaccine becoming available. BORN includes demographic data that allowed the research team to correct for smoking, education and income; however, as with any population-based study, it may not be possible to account for all influencing factors.
This study was funded by the Canadian Institutes of Health Research (CIHR). The Public Health Agency of Canada provided support to add the H1N1 questions to the BORN database. BORN is funded by Ontario's Ministry of Health and Long-Term Care, with its main offices based at the CHEO Research Institute.
Thanks to additional CIHR funding, the researchers are now following this cohort of children through their first year of life to assess possible longer term benefits of the vaccine.
The authors of "H1N1 Influenza Vaccination during Pregnancy and Fetal and Neonatal Outcomes" are: Deshayne B. Fell, Ann E. Sprague, Ning Liu, Abdool S. Yasseen, Shi-Wu Wen, Graeme Smith and Mark C. Walker.
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Ottawa Hospital Research Institute
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About the Ottawa Hospital Research Institute (OHRI)
The Ottawa Hospital Research Institute (OHRI) is the research arm of The Ottawa Hospital and is an affiliated institute of the University of Ottawa, closely associated with the university's Faculties of Medicine and Health Sciences. OHRI includes more than 1,500 scientists, clinical investigators, graduate students, postdoctoral fellows and staff conducting research to improve the understanding, prevention, diagnosis and treatment of human disease. Research at OHRI is supported by The Ottawa Hospital Foundation. www.ohri.ca
About the CHEO Research Institute
Established in 1984, the CHEO Research Institute coordinates the research activities of the Children's Hospital of Eastern Ontario (CHEO) and is one of the institutes associated with the University of Ottawa teaching hospitals. The Research Institute brings together health professionals from within CHEO to share their efforts in solving pediatric health problems. It also promotes collaborative research outside the hospital with partners from the immediate community, industry and the international scientific world. For more information, please visit www.cheori.org
About BORN Ontario
BORN Ontario gathers, interprets and provides access to trusted data for all births in Ontario—over 140,000 in 2011 alone. Comprehensive maternal-child health information is collected from screening programs, labour and birth hospitals and early childhood care providers. BORN's innovative technology and authoritative data, supported by and housed at the Children's Hospital of Eastern Ontario (CHEO), have contributed to true change, including hospital quality improvement projects, better understanding of outcomes associated with H1N1 vaccinations, and identifying missed opportunities for necessary care. As a prescribed registry with medical and technical leadership, BORN is instrumental in efforts to ensure the best possible beginnings for lifelong health. www.bornontario.ca
About the University of Ottawa
The University of Ottawa is committed to research excellence and encourages an interdisciplinary approach to knowledge creation, which attracts the best academic talent from across Canada and around the world. It is an important stakeholder in the National Capital Region's economic development.