US authorities announced Thursday they have halted clinical trials of an experimental vaccine designed to halt the virus that leads to AIDS after discovering it did not stop infection.

The program, which began in 2009, is the latest in a series of unsuccessful studies of candidate vaccines aimed at tackling HIV, the human immunodeficiency virus.

The National Institute of Allergy and Infectious Diseases said volunteers in 19 US cities -- either gay men or transgender people who had sex with men -- took part in the study, with the HVTN 505 vaccine given to 1,250 and 1,244 receiving a placebo.

A panel analyzed the results of the study on April 22 and recommended halting the program after findings indicated 41 infections among those who had received the vaccine versus 30 in the placebo group.

The NIAID, part of the National Institutes of Health that funded the clinical trial, said it planned to continue to follow the participants to further analyze the results of the study.

An estimated 34 million people are infected with HIV worldwide, including 3.4 million children.

AIDS has killed 30 million people since the beginning of the epidemic 30 years ago and an estimated 1.8 million people die from the disease each year.