Bleak shadow cast over fight against the Aids virus: Disappointment over AZT comes as hope of finding a vaccine has diminished. Steve Connor reports

THE virus that causes Aids is fast becoming the most-studied infectious agent. But the more we learn about HIV, the harder it is to find a way of fighting it other than with increasingly tired messages of safe sex.

Yesterday's announcement that AZT - the first drug to be licensed to treat Aids - is ineffective at preventing the development of the disease in healthy HIV-positive people comes just a week after scientists found that the virus was more active in the early stages than they had realised.

Rather than lying dormant in the 'latent' stage between infection and the onset of Aids (which can take many years), HIV has been found to be present in large quantities in the lymph glands, an important part of the body's immune system.

Researchers led by Anthony Fauci, from the United States National Institute of Allergy and Infectious Disease near Washington, reported in the science journal Nature that HIV is clearly active in the lymph glands of HIV-positive people throughout the latency period.

Another team of researchers, led by Ashley Haase of the University of Minnesota, found 'an extraordinarily large number' of blood cells of the type favoured by HIV infected 'from early to late stages of infection'.

The two sets of findings led scientists to call for the early treatment of people with the virus long before they develop Aids and even possibly as soon as they have become infected.

One hope for Aids was that it would be possible to delay the onset of the disease by extending the period of latency. But the outlook is bleaker now that the virus appears to become well established in a vital part of the body's defences soon after infection.

Most Aids researchers are convinced that it is vital to hit the virus early and hard if drugs are ever going to stand a chance of preventing the onset of the diseases that eventually lead to death. But, as the results of the AZT trial show, there is nothing as yet to hit it with.

One hope is to treat people with a combination of drugs, an approach that has shown promise in test-tube experiments. The theory is that while HIV can develop resistance to one drug, it will find it more difficult to become resistant to two or more drugs applied simultaneously. However, showing that drugs work in a test tube is far removed from success in patients vulnerable to side-effects.

If there is little prospect of anti-Aids drugs, the future for a preventive vaccine is even less promising. For such a vaccine to work, it must block HIV from becoming established in the lymph glands. Some scientists believe this will prove to be impossible and have called for vaccine research - which involves an expensive, elaborate testing process - to be abandoned and resources to be concentrated on developing anti-Aids drugs.

In the US, Howard Temin, a former Nobel laureate from the University of Wisconsin-Madison, and Dani Bolognesi, an Aids researcher from Duke University in North Carolina, wrote in a Nature editorial: 'A clear message from the new work is that HIV infection is a very complicated process and that it will require the march of science, frustratingly slow as it sometimes seems, to gain sufficient knowledge to control it.'