The US is finally joining the push for global vaccine access. It's almost certainly not going to be enough.

• President Biden committed the US to COVAX, the scheme to help poorer nations get vaccines.
• But the project is already struggling, and the details of the US contribution are vague.
• Experts see the scheme as the bare minimum, that will leave deep inequality even if it works.

As the world's rich countries place orders for enough coronavirus vaccines to inoculate their populations several times over, the World Health Organization has been pushing a scheme to get poorer countries access as well.

The scheme, called COVAX, hopes to distribute 2 billion COVID-19 vaccine doses worldwide by the end of 2021.

But it faces underfunding and supply issues, and the WHO has accused wealthy countries of hoarding doses and driving up prices, frustrating its progress.

COVAX just got a big boost: President Joe Biden's administration announced that it will support the scheme, a marked contrast with the Trump White House, which stayed out.

But experts and campaigners have noted that Biden's commitment is as yet poorly defined. At the same time the US government is on a vaccination drive as other nations struggle to get any doses at all.

The reality is that even with a US contribution, it is unlikely that vaccines will end up distributed in a way that would be widely seen as fair.

That failure is likely to have huge consequences - many thousands of deaths, deepening of global equality, and lingering outbreaks in poorer nations that could come back to bite even richer countries with widespread vaccination.

What exactly has Biden promised?

The day after Biden took office, Dr. Anthony Fauci of the US National Institute of Allergy and Infectious Diseases, said the Biden administration would join COVAX.

But the administration has given few specifics.

Kate Elder, senior vaccines policy advisor for Médecins Sans Frontières/Doctors Without Borders, told Insider that the US joining will be "invaluable."

But she and other experts warned that its help comes while vaccine supply is currently limited, meaning that extra money and resources will likely do little to address immediate need.

Professor Ken Shadlen, professor of Development Studies at the London School of Economics and Political Science, told Insider about some of the ways US participation may help.

He said funding from the US would help lower-income countries to purchase more vaccines, and perhaps better compete with richer countries who can pay more per dose.

But he also said that those efforts could be hurt by the lack of transparency around which countries have secured access to vaccines, and how much they are paying.

He said that, ultimately, the usefulness of US participation "depends on the size of the contribution," especially as the scheme struggles with existing problems.

Matthew McCoy, an assistant professor in the Department of Medical Ethics and Health Policy at the University of Pennsylvania, told Insider that the Biden administration joining COVAX is an "important step" in ensuring that the project meets its aims.

But he warned that the size of that impact "depends on the resources that the US commits to the initiative."

COVAX has problems to overcome

Reuters reported in December that COVAX faced a "very high" risk of failure due to underfunding and supply risks.

McCoy noted that COVAX could suffer more if wealthy countries continue to siphon off a large share of available vaccines, as they have been so far.

Countries like the US, UK, and Canada placed advance orders for enough doses to immunize each person who lives there several times over.

The logic is that the over-capacity will help countries ride of the risk of one vaccine not being approved, or some taking longer than expected to arrive. These countries are already fighting among themselves over who gets doses first.

McCoy and Elder said the US should do what Canada says it will do: donate the excess vaccines it has ordered to COVAX.

But that will be no help until those countries decide they don't need any more for themselves.

Elder also said that the plight of poor countries is arguably worse because of rich nations like the US pursuing their domestic vaccination programs so aggressively.

She said high-income countries had both "sucked up the supply" and "possibly driven up prices."

As a result, she said, COVAX "has very few tangible doses ready to distribute to the multitude of countries that are relying upon it."

Her warning mirrors that of Dr. Tedros Adhanom Ghebreyesus, the head of the WHO, who said countries were "going around COVAX, driving up prices and attempting to jump to the front of the queue."

Shadlen, the professor in London said that even if COVAX achieves all of its aims, inequality in vaccine access will still be vast.

"COVAX has very, very modest ambition, and so even if it works out exactly as planned, it's not going to plug the gap in vaccine inequality."

COVAX is the 'bare minimum'

Shadlen noted that many rich countries plan to vaccinate most of their adult population by the end of the summer.

But in contrast, he described COVAX's aim - to vaccinate around 20% of the populations of 92 countries by the end of the year- as "the bare minimum."

He said the scheme was set up to avoid the "worst-case scenario" in global inequality.

"But I just think that avoiding the worst case scenario should be understood as what it is: which is avoiding the worst case scenario."