The discovery of the virus that causes Aids in 1983 was hailed as a medical breakthrough. It had taken scientists only two years after the first reported deaths of homosexuals from a mysterious disease that destroyed their immune systems. No one would have expected, however, that HIV would have proved an elusive, mutating enemy that has since defeated the search for a vaccine at every turn. After all, the challenge of eradicating the virus was taken up by medical science, which had given us the miracle of antibiotics, eradicated the human scourge of smallpox and developed a vaccine against the crippling onslaught of polio. Yet, a quarter of a century later, the reality is that the world still has to live with Aids, at an unimaginable cost in human life and misery, as no cure has yet been found. So far, about 25 million people have died, with another 33 million infected. An arsenal of retroviral drugs has turned the killer virus into a manageable infection. Although they are now more affordable, most infected people in Africa, the front line of the Aids epidemic, are still not getting them. Even developed nations have not won complete victory over the cultural taboos, stigma, myths and complacency that plague the fight against Aids. Efforts to combat ignorance, complacency and cultural and political denial cannot be relaxed, because microbiologists say HIV may never be eradicated. In Hong Kong, the 414 new reported HIV cases last year was the highest since surveillance began in 1984, with the number attributed to homosexual and bisexual contact outnumbering those through heterosexual contact and drug injecting. It is all a reminder that the miracles of medical science are not to be taken for granted. We must safeguard our well-being with responsible behaviour, such as taking recommended precautions and heeding public health advice. Even antibiotics have been thrown onto the back foot by the emergence of resistant superbugs as a result of overprescribing. Even if the fight against HIV is won in the next 25 years, new strains of viruses and germs will continue to challenge medical science.