February 25, 2008
An Update Concerning the
HVTN 503/Phambili HIV Vaccine Study
In October 2007, NIAID and the HIV Vaccine Trials Network (HVTN) stopped immunizations and enrollment in the HVTN 503 (“Phambili”) HIV vaccine study in South Africa. The following are interim data concerning enrollment and the number of HIV infections in the Phambili study:
These data do not accurately reflect HIV incidence rates within the study because the duration of follow-up of the study volunteers varies considerably by individual and by group. In addition, behavioral risk factors, such as number of sexual partners, have not been accounted for.
To compare HIV incidence in the Phambili study to HIV incidence in the STEP (HVTN 502) HIV vaccine study will be difficult and may not be possible. The information collected after unblinding occurred may be considered biased by the fact that volunteers may have modified their behaviors based on their knowledge of whether they received the vaccine or the placebo. Further, without substantially more cases of HIV infection, it will not be possible to draw any scientifically valid conclusions about the vaccine’s effect on HIV acquisition.
NIAID and the HIV Vaccine Trials Network (HVTN) are committed to conducting further analyses to understand the findings from the HVTN 503 study and use them to inform future research on HIV vaccines. The study investigators will continue to follow all of the Phambili study volunteers and counsel them on how to reduce HIV exposure to limit the number of any new HIV infections.
Currently, other NIAID-sponsored vaccine studies involving Ad5 are paused or are proceeding only in individuals with Ad5 titers less than 18 units. For a complete listing of these studies, see Status of NIAID Adenovirus-based Vaccine Studies.
For more information about the Phambili and STEP HIV vaccine studies, see Immunizations Are Discontinued in Two HIV Vaccine Trials, An Update Regarding the HVTN 502 and HVTN 503 HIV Vaccine Trials and Questions and Answers: HVTN 502 and HVTN 503 HIV Vaccine Clinical Trials.
Media inquiries can be directed to the NIAID Office of Communications at 301-402-1663, firstname.lastname@example.org.
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Last Updated February 25, 2008