More than 32 years after the emergence of a fatal affliction of the immune system among clusters of young gay men in the US, World Aids Day has come around again without a cure or a vaccine in sight. Sex, age, social strata or sexual orientation make no difference. Some 35.3 million people around the world are now living with HIV or Aids, and there have been more than 25 million deaths from Aids-related causes, according to the World Health Organisation. A 30 per cent decline in Aids deaths in general populations from 2.3 million in 2005 to 1.6 million last year has not brought the dream of an Aids-free younger generation any closer. About one-seventh of all new HIV infections occur during adolescence, according to the UN children's agency Unicef, many in sub-Saharan Africa, because of barriers including harsh laws, inequality, stigma and discrimination which prevent people accessing services that could test for, prevent, and treat HIV. Nonetheless, countless millions remain alive today thanks to education and safe-sex practices that prevent infection, or advances in early drug treatment of HIV-positive people that delays the onset of Aids. All three factors resonate in Hong Kong. Contrary to reported experience in Asia generally, where young drug users account for most new infections, gay men in this city are still at the highest risk of contracting HIV, accounting for half of a record 153 new infections in the first three quarters of this year, according to the Health Department. If there is hope for HIV/Aids sufferers and those at risk, in the absence of a vaccine or a cure, it is to be found in studies that indicate the risk of infection can be reduced by more than 90 per cent by early treatment of people with HIV. Subject to the funding needed to expand access to drugs, and education to combat social and cultural factors that inhibit the delivery of treatment, medicines are on the threshold of achieving much of what a vaccine would.