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

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."