The first clinical trials to study the new pandemic H1N1 flu vaccine in HIV-positive pregnant women and HIV-positive children and adolescents starts this week, according to an announcement by the National Institute of Allergy and Infectious Diseases (NIAID).

Both pregnancy and HIV infection can decrease the immune response to vaccines. For this reason, both studies are looking at doses of the H1N1 vaccine that are higher than the 15 microgram dose being given to the general population.

One of the trials will enroll 130 HIV-positive pregnant women between ages 18 and 39 who are in the later months of their pregnancy, while the other trials will enroll 140 children and young people between ages 4 and 24 who were infected with HIV at birth. Both the women and the youth will receive two 30 microgram doses at 21 days apart.

“These studies are important because HIV infection and pregnancy both increase the risk for a poor immune response,” explained Anthony Fauci, MD, the director of NIAID. “Moreover, children, young people and pregnant women are at higher risk for more severe illness from the 2009 H1N1 influenza virus than other groups, and HIV-infected individuals in these populations may be particularly vulnerable.”