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Link between influenza vaccination in pregnancy and reduced risk of premature birth

Press release from PLoS Medicine


A study published in this week's PLoS Medicine suggests that there might be an association between maternal immunization with inactivated influenza vaccine during pregnancy and reduced likelihood of prematurity and the baby being small for gestational age.

The study, led by Saad B. Omer from the Emory University Rollins School of Public Health in Atlanta, Georgia, used a large surveillance dataset (the Georgia Pregnancy Risk Assessment Monitoring System) to analyze the relationship between receipt of inactivated influenza vaccine during any trimester of pregnancy by mothers of infants born between June 1, 2004 and September 30, 2006 and their baby being premature and small for gestational age: 4,168 mother-baby pairs were included in the analysis.

The authors found that babies who were born during the influenza season (October-May) and whose mothers were vaccinated against influenza during pregnancy were less likely to be premature compared with infants of unvaccinated mothers born in the same period with an adjusted odds ratio of 0.60. Compared with newborns of unvaccinated women, babies of vaccinated mothers had lower risk of being small for gestational age during the period of widespread influenza activity but the researchers did not find a statistically significant effect on small for gestational age babies during the other periods (pre-influenza activity period, local and regional influenza activity periods).

As an observational study, the work can only show there is an association between influenza vaccination and reduced risk of prematurity, and cannot demonstrate there is a causal link. The authors add "Studies in other populations, particularly randomized controlled trials, are needed to confirm our results."


Funding: The study was partially funded through the Emory University, Global Health Institute Faculty of Distinction Fund award (recipient: SBO). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

Competing Interests: SBO was awarded the Maurice R. Hilleman Early-stage Career Investigator Award by the National Foundation for Infectious Diseases. The award is funded by an unrestricted educational grant to the National Foundation for Infectious Diseases from Merck and Co., Inc. However, SBO had no direct interaction with Merck related to this award. The other authors report no competing interests.

Citation: Omer SB, Goodman D, Steinhoff MC, Rochat R, Klugman KP, et al. (2011) Maternal Influenza Immunization and Reduced Likelihood of Prematurity and Small for Gestational Age Births: A Retrospective Cohort Study. PLoS Med 8(5): e1000441. doi:10.1371/journal.pmed.1000441

Saad B. Omer
Emory University, Rollins School of Public Health
Hubert Department of Global Health
1518 Clifton Road NE
Room 750
Atlanta, Georgia 30322
United States of America
+1 404 727 9814

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