By Martin Hutchinson
BBC News Online health reporter
President Bush has signed into law a $15 billion package of measures to help prevent and treat Aids in poor countries.
Bush pledged billions for HIV control
He hailed the programme as a "great mission of rescue" - but what impact will the money have?
The scale of the HIV epidemic in the developing world is difficult to conceive from the relative safety of the West.
In turn, this hardly makes it a priority for the average voter, keeping it low on the political agenda.
All of which made one of the central policy announcements of George W Bush's State of the Union address earlier this year - funding for a massive anti-HIV programme - all the more surprising.
"Seldom has history offered a greater opportunity to do so much for so many," he said.
His "Emergency Plan" will involve approximately $3 billion a year for the next five years to be spent both on providing medicines for those who already have HIV, and trying to prevent new infections.
This is perhaps not entirely altruistic - UNAids believes that the economic effects of an unchecked Aids epidemic in Africa and beyond will ripple out to hurt Western economies before long.
The extra money will undoubtedly have a significant impact on the disease in sub-Saharan Africa and the Caribbean.
However, experts say that even this fortune may not be enough to prevent the epidemic running out of control for years to come.
And there is nothing for India, and other parts of the world where new HIV infections are predicted to rise sharply over the next five years.
Aids will only be defeated when responsibility for addressing it is fully shared
Currently, researchers predict that, by 2010, there could be 45 million new HIV infections worldwide if the disease spread is not slowed.
In 2002, UNAids calculated that $10 billion should be spent each year in less-developed countries to produce even an "adequate" response to HIV.
Even with the Bush billions, the total falls well short of this.
Dr Peter Piot, the executive director of UNAids, said: "There is still a long way to go.
"Aids will only be defeated when responsibility for addressing it is fully shared - with every nation working to meet the financial and leadership challenges presented by this global epidemic."
While there are calls for the US to increase the size of the programme yet further, there remain doubts about whether the Bush administration will be able to deliver the funds in an effective way to the countries - and projects - where it is needed.
An analysis by the Global Aids Alliance suggests that the billions are to be phased in gradually, with just over $2 billion made available in 2004, rising to $3.8 billion in 2008.
"This is inappropriate from a public health standpoint," it says, "because the epidemic is expanding exponentially now and there is extensive underfunding of currently available programmes that are ready for scale-up".
There are also concerns that the programme has been left slightly hamstrung by a concession made by President Bush to lobbyists.
This stipulates that a third of the money designated to prevention work must be spent promoting sexual abstinence prior to marriage as a method of protection.
This approach is seen by public health experts as less effective than promoting the use of condoms and other safe sex practices.
Congress has to approve each year's allocation for the programme, and some in Washington are expressing doubt over whether future year's billions can fit within tight budgets set for foreign aid by the Republicans.
While the new law allows for up to $15 billion over the five year period, it does not bind the administration to this amount - the administration could trim the programme in future years if it wished.
Despite reservations from some on the front-line of the fight against HIV - there is little doubt that most in the field are delighted with such a major commitment from the world's largest power.
It could help provide leverage to elicit billions more in pledges from other developed nations over the next few years.
The UK has allocated no new money for HIV/Aids abroad since 2001, and activists are hopeful that the upcoming meeting of G8 nations will be the venue for its own announcement.
Campaigners say that action to cancel the debts of some of the worst-hit countries could make the programmes yet more effective - as would further significant price reductions in the cost of vital drugs.
They point out that the US, in the past, has supported moves to prevent poorer countries making their own cheap generic versions of anti-HIV drugs.
But, amid the calamity that has befallen entire generations in some African states, there is reason for some optimism.
Some sub-Saharan African countries are already showing that well-funded, carefully targeted prevention campaigns can have a pronounced effect on the rate of new infections.
If the money is spent well, the expectation that many lives will be saved is entirely justified.