It is man-made by genetic engineering in the lab, and consists of only a few proteins that cannot multiply in your body. We expect that the vaccine will cause the immune system to produce antibodies or T-lymphocytes, which can Suppress or kill HIV if the person is ever exposed. At this stage, all results come through blood tests or other laboratory tests that measure the immune response. All vaccines are tested in animals first. When we test them in humans, we start with very small doses, then monitor the volunteers for side effects as we increase the dosage.
Most people can expect a sore arm for a day or so.
A few people may also have mild flu-like symptoms. We do not know of any more serious reactions, but they are theoretically possible. Some people may have a false positive test on the most common blood tests for HIV, because they develop antibodies to the vaccine. There are other tests that can prove you are not really infected. It is not possible to pass on antibodies to someone else.