The Covax scheme launched a push for an extra $2 billion in donations on Thursday, saying it needed the money in advance to reserve Covid-19 vaccine doses.

The Covax facility ensures the 92 poorest participating economies can access coronavirus jabs, with the cost covered by donors.

The United States co-hosted Thursday's donor event at which the first $400 million was raised.

Sweden led the way, putting in $258 million, with the Netherlands donating $47 million.

"People everywhere should have access to rigorously tested, safe, and effective Covid-19 vaccines," said US Secretary of State Antony Blinken.

"As long as Covid is spreading and replicating anywhere, it poses a threat to people everywhere."

Japanese Prime Minister Yoshihide Suga will host a Covax funding summit focused on the 92 countries in June, it was announced.

"The supply of vaccines and funding are still insufficient, and there is an urgent need to further strengthen the Covax facility to ensure equitable access to safe, effective, and quality-assured vaccines to people in developing countries," said Japan's Foreign Minister Toshimitsu Motegi.

Nearly 840 million doses of Covid-19 vaccines have been administered in at least 205 territories around the world, according to an AFP count.

Covax has delivered more than 38 million doses so far to 113 participating territories.

The first shipment landed in Ghana on February 24, with Ghanaian President Nana Akufo-Addo publicly taking the first shot.

Covax is co-led by the WHO, the Gavi vaccine alliance, and the Coalition for Epidemic Preparedness Innovations.

The scheme is aiming to distribute enough doses to vaccinate up to 27 percent of the population in the 92 poorest participating economies by the end of the year.

"We have now secured up to 2.5 billion doses ... and sight on another billion doses," said Gavi chief Seth Berkley.

"You can put advance purchase agreements in place but to do those you have financing available.

"That's why the up-front money is critical."

Sweden's donation made it the largest contributor relative to population.

"This is an investment not only in global solidarity, but also in our common objective of putting an end to the pandemic," said International Development Minister Per Olsson Fridh. 

"Minimising the risk of dangerous virus variants, enabling a quicker economic recovery and minimising the already devastating impact of Covid-19 is in everyone's best interest," he said.