A new vaccine for HIV is raising excitement after its first in-human trials showed 97% success at stimulating a rare set of immune cells that play a key role in fighting the virus. 

The vaccine approach is a new attempt to head off the fast-mutating human immunodeficiency virus, which has eluded vaccines in the past because it attacks part of the immune system directly and is good at evading other immune defenses. Developed by scientists at Scripps Research in San Diego and the nonprofit International AIDS Vaccine Initiative (IAVI), the vaccine is in Phase I clinical trials and has been tested in only 48 people so far.