GAVI is a public-private partnership backed by the Bill & Melinda Gates Foundation, the World Health Organization, the World Bank, UNICEF and others, which arranges bulk buys to reduce vaccine costs for poor countries.

Speaking to Reuters last week Berkley said he was encouraged by the sheer number of potential COVID-19 vaccines in the early stages of development around the world, which he said would slim down to a smaller number as some progressed and some failed.

"Today there are 76 vaccines on WHO website listed, of which six are already in clinical trials, but actually the number is substantially higher than that, it is well over 100," he said.

"That is really good, because what is bubbling up is science from around the world.

"The challenge is going to be now, once all of the science bubbles up, is to have some standardised criteria that one can narrow it down to a smaller number. And what is going to be important is being able to make those choices based on science and not politics."

GAVI said this month it planned to disburse $29 million to support health systems in 13 lower-income countries to fight COVID-19.