GENEVA (REUTERS) - Wealthier countries that join the World Health Organisation's (WHO) Covid-19 vaccine plan are being offered a new option to pick and choose which shots they get while reserving a right to receive their "full share" of doses, documents seen by Reuters show.

The change appears aimed at convincing governments which have negotiated their own bilateral deals securing experimental vaccines to also sign up for the global Covax facility by next Monday's (Aug 31) deadline for submitting expressions of interest.

"They are trying to be more flexible for self-financing countries to make it more interesting... There are some advantages to incentivise you to pay upfront," said a Western diplomat familiar with the terms.

The United States, Japan, Britain and the European Union have struck their own deals to secure millions of Covid-19 vaccine doses for their citizens, ignoring the WHO's warnings that "vaccine nationalism" will squeeze supplies.

The WHO did not respond to a request for comment. Reuters could not determine if the documents were the final offer. The document with the new terms and conditions was dated Aug 5.

The offer is the latest sign of concern in the UN agency about its effort to unite the world behind its vaccine as it struggles to get wealthier countries on board beyond pledges of funding and warm words about donating surplus vaccines.

It's not clear if the new terms will be enough to win back the EU, which has told member states they can help fund the programme but can't seek to buy vaccines via both schemes.

The latest WHO plan, circulated to its 194 member states in the last days, promises to "negotiate the best possible pricing from manufacturers" and to establish a "marketplace" for trading or selling doses.

The deadline for confirming commitment is Sept 18, with upfront payment due by Oct 9.

'OPTIONAL PURCHASE'

The Covax facility, launched in late April, is designed to serve as an "invaluable insurance policy to secure access to safe and effective Covid-19 vaccines" through a portfolio of experimental vaccines using a broad range of technologies, the WHO said. For now it relies on nine experimental vaccines.

It aims to deliver at least two billion doses of approved vaccines by the end of 2021 and to ensure "equitable access".

Through the WHO's standard "Committed Purchase" arrangement already on offer, self-financing states are to make a lower upfront payment of an estimated US$1.60 (S$2.18) per dose, plus a US$8.95 financial guarantee per unit, but have to make firm guarantees to buy doses, it said.

If the final price exceeds double that total of US$10.55 per dose, or US$21.10, countries are allowed to drop out, it said.

Under the new "Optional Purchase" arrangement, their higher upfront payment is US$3.10 per dose. This covers their full pro-rata share of the investments required by the Covax facility to enter into agreements with manufacturers and accelerate scale of production and access, it said, adding that the estimated all-inclusive cost per dose might still be US$10.55.

"These participants have the possibility to opt out of vaccine allocations while still reserving their 'options' to receive doses of a subsequent vaccine being provided through the Facility," the WHO said.

"This option may be more attractive for countries that already have bilateral deals in place and may not be interested in acquiring more of those vaccines."

While a country exercising this option retains an ability to receive its full share of doses, it should recognise that opting out of a particular vaccine "may delay the time until a country receives doses, particularly in the initial phase where there may only be one or two vaccines and the quantities will be limited".

The optional scheme would cost an estimated US$262.8 million based on a country with a 60 million population electing to cover 20 per cent of that and a two-dose regimen, the WHO document said.

The standard one would cost US$253.2 million.

So far some 172 countries have registered expressions of interest, including 92 low- and middle-income countries eligible to secure doses through the Gavi vaccine alliance which covers much of their cost.

Some 80 potentially self-financing countries have submitted expressions of interest.

"No self-financing participant will receive doses of vaccine to cover greater than 20 per cent of its population until all self-financing participants have either also been offered doses in an amount to achieve 20 per cent coverage or hit their elected quantity (if lower than 20 per cent)," the WHO said.