JAMA   
July 11, 2012, Vol 308, No. 2
http://jama.ama-assn.org/current.dtl

Editorial | July 11, 2012
Influenza Pandemics—Pregnancy, Pathogenesis, and Perinatal Outcomes
Mark C. Steinhoff, MD; Noni E. MacDonald, MD, MSc, FRCPC

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Since the 1918 influenza pandemic, it has been clear that pandemic influenza is associated with increased morbidity and mortality in pregnancy, and more recent studies have shown that nonpandemic seasonal influenza strains also lead to morbidity for pregnant women and their infants.1 In the 2009 worldwide pandemic of influenza A(H1N1)pdm09, pregnant women were at high risk for severe complications, including death and intensive care unit admission.2

The adverse effects of antenatal influenza infection on pregnant women and their infants suggest a biological effect of influenza infection in the mother that compromises the fetus. These effects are rarely associated with direct infection of the fetus with influenza virus, although fetal infection has been reported infrequently during epidemics, pandemics,3 – 4 and with the H5N1 influenza strain.5 Instead, it appears that the normal pregnancy-associated immunologic changes may inhibit the inflammatory response to influenza virus infection in pregnancy,6 leading to increased risks to mother and infant. Because of these observations, pregnant women have been listed among high-risk groups for seasonal influenza vaccine in the United States since 1997, and safety data suggest these vaccines are safe in pregnancy.7 – 8 Pregnant women were prioritized for immunization during the 2009 influenza A(H1N1)pdm09 pandemic, despite limited data on the safety of pandemic influenza vaccines in pregnancy.

In this issue of JAMA, Pasternak and colleagues9 report the results of an observational cohort study on the safety in pregnancy of the monovalent inactivated ASO3-adjuvanted split virion influenza A(H1N1)pdm09 vaccine…