The STEP Study HIV vaccine trial

In May 2006 an international HIV vaccine trial will begin recruitment in Sydney. The trial will have 3,000 participants in all, with about 100 from Sydney. Other trial sites are in US, Canada and South America.

What does the STEP Study test?

The STEP study is intended to test whether the vaccine provides any protection from HIV infection or disease. Information on its safety profile will also be collected.

What does ‘HIV infection or disease’ mean?

It is possible that the vaccine might prevent infection. It is also possible that vaccinated individuals who are subsequently exposed to HIV will get infected, but that the vaccine will assist their immune systems to control the infection better, suppressing viral load and delaying HIV-related disease.

The third possibility is that the vaccine will have no effect on HIV infection or HIV disease.

Who can participate?

People in good health who live in Sydney and are at high risk of acquiring HIV are eligible to participate.

How is ‘high risk of HIV’ defined and assessed?

Current Australian research informs the definition of high risk, which comprises:

• Women and men who have an HIV positive regular sexual partner;
• Women and men who have ever taken non-occupational PEP (post-exposure prophylaxis);
• Men who have had unprotected anal sex in the last six months; and

• Men who have had an anal sexually transmissible infection in the last year.

Does everyone on the trial get the vaccine?

Half of the participants are injected with the experimental vaccine, while the other half are injected with an inactive substance that looks like the vaccine (placebo). Participants will not be told which one they have been given.

How does the trial get a result?

About 3,000 people worldwide will take part in the STEP Study. Participants are recruited because their current behaviour indicates they are at high risk of acquiring HIV infection. While trial participants will be counselled to practice safe sex/safe injecting while on the trial, it is expected that a certain number of participants will have unsafe sex and contract HIV despite this counselling. The results of those who received the vaccine will then be compared with the results of those who did not.

Can people get HIV from taking the vaccine?

It is not possible to become HIV infected from taking the study vaccine.

Who is conducting the trial?

The STEP Study is a collaborative effort. In Australia it is being conducted by the National Centre in HIV Epidemiology and Clinical Research through St Vincent’s Hospital, Darlinghurst. The Australian Federation of AIDS Organisations has been involved in its planning and oversight. The experimental vaccine was developed by Merck & Co. Inc and funding for the trial is provided by Merck Sharp& Dohme (Australia) Pty. Ltd.

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