ALVAC 1433 is an experimental therapeutic vaccine tested in people with HIV. Therapeutic vaccines are being developed for use in HIV-infected people to stimulate the immune system and slow the progression of HIV disease.

ALVAC 1433 is a canarypox virus, which has been genetically engineered to carry HIV genes such as env and gag, and to express molecules that will trigger HIV-specific immune responses.

It is being developed by French researchers from the Agence Nationale de Recherches sur le SIDA (ANRS) and other institutions. ALVAC 1433 is also known by the longer name ALVAC-HIV vCP1433.

ALVAC 1433 has shown the most encouraging results of all the therapeutic vaccines to date. Not only has immunisation in HIV-infected people stimulated HIV-specific immune responses, it has produced better treatment responses in patients who have ceased their antiretroviral therapy. There is also evidence that it may reduce the viral load ‘set-point’ during an interruption of antiretroviral therapy, suggesting better control of HIV by the immune system.

In the major study of the vaccine, 70 patients were randomised to continue taking antiretroviral therapy, or to add four cycles of ALVAC 1433 and the vaccine Lipo-6T over twelve weeks followed by three cycles of interleukin-2 (Proleukin). At 40 weeks, the 63 patients with undetectable viral loads stopped antiretroviral therapy, but those who received the vaccine took longer to experience a rebound in viral load and were more likely to be off therapy after twelve weeks, even after controlling for immune responses at the start of the study and previous exposure to interleukin-2^[1][2].

The vaccine is safe, with few side-effects in patients taking antiretroviral therapy^[3].