Because the vaccine contains inactivated virus, it is impossible to become infected with the 2009 H1N1 influenza virus by receiving this vaccine. The vaccine contains no thimerosal, a preservative, or adjuvant, a substance added to some vaccines to improve the body's response to vaccine.

The design of this trial in pregnant women is patterned after clinical trials that opened in August through NIAID's VTEU network. Those trials are testing the same vaccine in various groups of healthy individuals, including adults, the elderly and children. The candidate vaccine is also being tested in pregnant women because they represent a population who public health officials have recommended to receive a licensed 2009 H1N1 influenza vaccine when it becomes available this fall.

The trial is taking place at the following six medical centers: Baylor College of Medicine VTEU in Houston; Group Health Cooperative Center for Health Studies VTEU in Seattle; Saint Louis University VTEU; Vanderbilt University VTEU in Nashville; Duke University in Durham, N.C.; and Scott and White Memorial Hospital and Clinic in Temple, Tex.

Source: NIH/National Institute of Allergy and Infectious Diseases