a group of activists and health professionals in the us have offered to test a controversial aids vaccine on themselves. Their offer is a part of a calculated effort to break the deadlock that has frustrated researchers since the start of the aids epidemic. Scientists know vaccines are the best way to stop the spread of a deadly virus, but there is no way to determine how effective a vaccine is in humans without putting some humans at risk.

Ronald Kesrosiers, a professor of microbiology at Harvard Medical School in the us injected a handful of chimpanzees with a solution of weakened hiv . After a year, he exposed them to the full-strength virus. Every chimp had an immune response strong enough to contain the killer virus