The study team will take blood samples from the pregnant women after each dose and three and six months after delivery to measure the concentration of antibodies the women produce against 2009 H1N1 influenza virus and how strong that antibody response remains over time. After the women give birth, study staff will sample umbilical cord blood to measure the concentration of maternal antibodies against the H1N1 virus that were transferred to the infants through the placenta. The study team also will collect small blood samples from the infants at 3 and 6 months of age to measure their level of maternally derived antibody protection from the virus over time. The infants will not receive vaccine.

Similarly, in children and young people, the strength and longevity of the immune response will be gauged by testing blood samples taken 21 days after the first dose, 10 days after the second dose, and six months after entering the study.

The vaccine, manufactured by Novartis Vaccines and Diagnostics, contains inactivated 2009 H1N1 influenza virus, so it is impossible to become infected with the virus by receiving the vaccine. The vaccine does not contain adjuvant, a substance added to some vaccines to improve the body's response to vaccine.

Research on seasonal influenza vaccine and vaccines for other diseases in HIV-infected and other populations suggest that higher doses of vaccine tend to elicit stronger immune responses. These stronger responses, in turn, increase the concentration of protective antibodies in the bloodstream, which likely is beneficial to both the vaccinated individual and, if pregnant, to her fetus. This is the rationale for testing whether higher doses of licensed 2009 H1N1 influenza vaccine elicit a protective immune response in HIV-infected individuals and whether that protection is transferred to the fetuses of vaccinated pregnant women.

Source: NIH/National Institute of Allergy and Infectious Diseases