LONDON — More than 70 rich countries have signed up to a global coronavirus vaccine initiative intended to ensure that any effective shots are fairly distributed around the world - but which may also allow them to buy more vaccines to stockpile for their own citizens.

In a statement on Wednesday, the vaccines alliance Gavi reported that 75 countries have said they would join its new "Covax facility" along with another 90 low-income countries that hope to receive donated vaccines. The Associated Press reported this week that the Gavi initiative may allow rich countries to reinforce their own coronavirus vaccine supplies while leaving fewer doses available for more vulnerable populations.

When Gavi approached donor countries last month, it advertised the plan as an "insurance policy" for rich countries that have already struck deals with drugmakers for experimental COVID-19 vaccines.

Gavi told donor governments that when an effective inoculation is found within its pool of COVID-19 candidates, all countries will receive enough to cover 20% of their populations, including rich countries that may have their own stockpiles. It said countries would be encouraged, but not required, to give up any doses they might not need.

"For the vast majority of countries, whether they can afford to pay for their own doses or require assistance, it means receiving a guaranteed share of doses and avoiding being pushed to the back of the queue," Gavi CEO Seth Berkley said in a statement.

Dozens of vaccines are being researched, and some countries — including Britain, France, Germany and the United States — already have ordered hundreds of millions of doses before the vaccines are even proven to work.

Critics say offering rich countries the chance to buy even more vaccines through Gavi essentially allows them to hoard limited COVID-19 vaccines without consequences.

Gavi CEO Berkley acknowledged there was no enforcement mechanism, but he said the alliance would be speaking with rich countries to propose possible solutions.

Gavi said the 165 countries that have expressed interest represent about 60% of the world's population. The alliance is aiming to raise $2 billion to buy COVID-19 vaccines.