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HIV Vaccine Study Halted as Too Logistically Complex

A vaccine that will prevent infection by the human immunodeficiency virus (HIV) is thought to be the best hope for ending the HIV/AIDS pandemic sweeping the globe and the Vaccine Research Center (VRC) has developed one said to be scientifically intriguing and different enough from vaccines that have been previously explored that further testing is highly desired.  Plans for a widespread test of the vaccine have been halted now for a second time, however, due to concerns stemming from a previous trial of another vaccine that failed to reduce viral load as expected.

Viral load, the bloodstream’s saturation level of HIV in people who were vaccinated before becoming infected with the virus, is the focus of the PAVE 100 study, just as it was the focus of the STEP trial before it.  The STEP trial was halted before completion because the vaccine under study in that trial did not prevent infection with HIV nor did it sufficiently reduce viral load.

Even though the PAVE 100 trial was slated to use a different vaccine, representatives from both the scientific and the HIV advocacy communities called upon the National Institute of Allergy and Infectious Diseases (NIAID) to stop the PAVE 100 trial before it got started.  The VRC, which developed the vaccine under question, is a part of the NIAID, which is, in turn, a part of the National Institutes of Health (NIH).

As originally planned, the PAVE 100 study would have involved 8,500 volunteer study participants in the United States, the Caribbean, South America, and Africa and was scheduled to begin the volunteer recruiting phase in October 2007.  Recruitment was postponed, however, when the STEP vaccine study was halted because it was found to actually cause more HIV infection in the test group receiving the vaccine than in the control group receiving placebo vaccines.  The STEP vaccine manufacturer, Merck & Co., Inc., claims its vaccine did not actually cause infection and only a specific group of study participants became infected.

The STEP vaccine did not prevent HIV infection in male study participants who were uncircumcised and also had a specific preexisting condition which neutralized antibodies to a virus known as adenovirus type 5 (Ad5), which causes the common cold.  The Ad5 was used as a carrier for the HIV gene in the vaccine, as it is in the PAVE 100 vaccine.  There was no evidence of increased rates of infection in men who had been circumcised and in those who did not carry the antibodies that neutralize Ad5.

Once the STEP study was halted, the PAVE 100 was downscaled to include just 2,400 men in the US who were circumcised, had sex with men, and who did not carry the antibodies that neutralize Ad5.  The revamped study was to have tested the vaccine’s ability to reduce viral load, examine detailed immune response to the vaccine, and provide information regarding the vaccine’s safety.

Critics of the downscaled PAVE 100 study asked that it be canceled before getting started because it is still so complex on both the scientific and logistic fronts.  Although NIAID has agreed to stop the PAVE 100 trial at this time, it is entertaining the idea of an even further downscaled version of the study in which only one aspect of the vaccine will be studied - that of lowering the viral load.  Should the next revamped trial of the PAVE 100 vaccine prove to be effective at significantly lowering viral load, NIAID will likely proceed with further, broader, studies of the vaccine.

Source: National Institute of Allergy and Infectious Diseases

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