昨天是世界艾滋病日，在过去的20年里，国际社会为防治艾滋病做出了不懈努力，并取得积极进展。全球艾滋病防治在2007年首次出现了“明显的重要进展”，艾滋病病毒新感染人数和死亡人数都有所下降。今年世界艾滋病日的主题仍为“领导”，意在突出领导者在艾滋病防治中的作用，宣传口号为“遏制艾滋、履行承诺”。

As World AIDS Day is marked on Monday, the fight against the disease remains¹ stymied² by the lack of adequate treatment in poor countries and setbacks in finding an effective vaccine³, experts say.

To be sure, there have been plenty of advances over the past two decades. While 33 million people have the human immunodeficiency virus (HIV) virus that causes AIDS, more are enjoying healthier, longer lives thanks to powerful new medications.

Organisers of World AIDS Day -- built around the themes of leadership, self-responsibility and activism -- are calling on governments to follow through on promises of universal treatment, prevention, care and support.

"We have effective treatments. We have no other choice than to offer them to all those who need them," said Jean-Francois Delfraissy, head of the French National Research Agency on AIDS and viral hepatitis (ANRS).

But affordable⁴ and effective treatment remains a rarity in Africa, home to the majority of HIV-positive people, making prospects⁵ of universal access to medication remote in the near future.

In poorer countries, the choice may eventually be between treating millions of HIV-positive patients, or offering more expensive treatment to some 500,000 people who are resistant⁶ to mainstream⁷ therapies, Delfraissy said.

Even in wealthier nations like France, where 5,200 new HIV-positive cases were registered last year, thousands of others remain unaware⁸ they are infected.

"Don't let AIDS pick up speed!" urges the French association AIDES, which plans to install a huge counter on the Paris opera house showing the lag between new infections and treatment.

On Friday, the United Nations urged countries to focus on the roots of the epidemic⁹ and draw on a panoply¹⁰ of tried-and-tested tools to help HIV from spreading among people most at risk.

"There is no single magic bullet for HIV prevention," said outgoing UNAIDS executive director Peter Piot.

Hopes for such a magic bullet were shattered last year, when scientists were forced to abandon two advanced clinical trials of an AIDS vaccine by pharmaceutical¹¹ company Merck, after they appeared to actually heighten the risk of infection.

But AIDS research was given a boost in October when the 2008 Nobel Medicine Prize was bestowed¹² to a pair of scientists who discovered HIV.

Researchers have also discovered new molecules¹³ and have launched tests on new triple treatments that have proved effective for patients no longer responding to other therapies.

Meanwhile, research on finding an effective AIDS shot continues. US scientists recently discovered a gene¹⁴ that may pave the way for a vaccine.

Delfraissy, of ANRS, also predicts a revival¹⁵ in basic research to find molecules capable of attacking the virus at a stage where it has not yet been detected.

Scientists are also interested in the cases of some HIV-positive people who never develop full-blown AIDS.

"We have an impressive arsenal," said Father Pierre-Marie Girard, who heads the infectious disease unit for the Saint Antoine Hospital in Paris.

One mark of success, he said, is those with HIV today talk of living and aging well with the virus -- with hopes of enjoying the same lifespan as those without.