The success of an experimental vaccine trial with rhesus monkeys is motivating a pharmaceutical company to undertake experimental HIV vaccine tests in Thailand, East and South Africa, and the United States of America US, with 400 healthy participants taking part in the first phase of the trials. Scientists say the vaccine protected half of a batch of monkeys against the Simian Immunodeficiency Virus, SIV, which is very similar to HIV, the virus that causes AIDS.