As part of the study, Rhesus monkeys were given three separate doses of the vaccine, which was prepared by USP scientists at varying intervals since last November. The study is being conducted at the University's Butantan Institute, a world leader in pioneering vaccines and anti-venoms.

The immunizing component of the vaccine has been developed and patented by the leading Brazilian university.

“We tested the immune response of the [monkeys] and the results were excellent,” lead vaccine developer Edécio Cunha Neto told Brazilian newspaper Folha de S.Paulo.

The scientists said they were surprised by the results and by how intense the response was in primates, after more muted results from tests on rats. Vaccine responses are usually expected to be lower in primates than in rodents, but in this case the primate responses were up to ten times higher, scientists said.

Human vaccine against HIV/AIDS?

The scientists' say their goal is to create a safe and effective human vaccine that will immunize people against the virus which, if not kept at bay by antiretroviral drugs, leads to AIDS.

Figures from the World Health Organization show that AIDS killed around 1.6 million people worldwide in 2012, and that 35 million people are currently living with HIV/AIDS.

Researchers developing the vaccine since 2002 first looked at human patients whose own immune systems were capable of recognizing and fighting HIV, allowing them to work out which peptide components of the virus were triggering by a response from the body.

This breakthrough gave a rise to a targeted DNA vaccine, which has been tested on rodents modified to replicate human immune responses, and now primates.

Researchers are looking to put the vaccine technology into a host virus which would be unable to infect the individual with HIV but would give greater immunization.

The next stage for the vaccine will see it given to 28 of the rhesus monkeys to compare immune responses depending on a set of variables over two years. This development phase on monkeys is expected to last until 2016.

Financial and ethical cost

The first dose of the HIV vaccine was given to healthy primates at the beginning of November 2013 in conjunction with a flu-like virus, which scientists say catalyzes a greater immune response.

The enclosure housing the monkeys at the Butantan Institute has been subject to tighter security since the beginning of trials due to increased activity by animal rights campaigners, who have questioned why the tests have to be carried out on primates.

However, researchers say that the final human destination for the vaccine means primates must be used in its development, given their genetic closeness to humans, but have stressed that the animals taking part in the experiments are well treated.

Eventually it is hoped to move the study onto a human testing phase, although the university is still looking for private investors; it is expected to cost around 250 million Brazilian reais (approximately US$105 million) to develop.

The study has so far cost around 1 million reais (US$419,000), reports say.

Other HIV vaccines are in different phases of development across the world, and hundreds of millions of dollars are being spent annually on this medical Holy Grail.