Prime Minister Boris Johnson will announce on Friday that the U.K. will donate surplus coronavirus vaccines to developing countries to boost the global battle against the Covid-19 pandemic.

The “majority” of any future U.K. surplus coronavirus vaccines will be shared with the World Health Organization-backed Covax program, Johnson’s office said late Thursday in a statement. That’s on top of the $766 million the country has already donated to the program, which is aimed at supplying some of the world’s poorest nations with inoculations.

Johnson on Friday will host a video call among the leaders of the Group of Seven nations, during which he’ll encourage them to increase their Covax funding, according to the statement. He’ll also call on his counterparts to back efforts to speed up the development of vaccines for new diseases, setting a target of slashing the period to 100 days from the approximately 300 days it took to develop coronavirus vaccines.

While France is committing to donate 5% of its vaccine supplies to Covax, Johnson’s office didn’t say how many vaccine doses the U.K. is prepared to contribute from the U.K. stock.

The U.K. has already secured more than 400 million doses from seven manufacturers to vaccinate its population of 67 million people. An assessment will be made later in the year to determine what can be donated to Covax, based on supply chain reliability and whether new vaccines are needed to tackle variants or as booster doses in the fall.