LONDON -- Britain is in talks with AstraZeneca for additional doses of its COVID-19 vaccine that will have been modified to better target the Beta coronavirus variant first identified in South Africa, health minister Matt Hancock said on Wednesday.

Britain has previously secured 100 million doses of the vaccine, developed at the University of Oxford and licensed to AstraZeneca.

"We've started commercial negotiations with AstraZeneca to secure a variant vaccine: future supplies of the Oxford AstraZeneca vaccine that have been adapted to tackle the B.1.351 variant first identified in South Africa," Hancock said in a speech at the university.

South Africa put use of AstraZeneca's shot on hold in February after data showed it gave minimal protection against mild-to-moderate infection caused by the country's dominant variant, now known as Beta.

Oxford considers the variant top priority for vaccine developers, and AstraZeneca has targeted the development of new vaccines against variants by the autumn.

Britain has committed to funding trials for the new adapted vaccine, which could be fast-tracked through the regulatory process following new guidance in March.

Hancock's speech came before he hosts a summit of Group of Seven (G7) health ministers in Oxford, which starts on Thursday.

He said that Britain had hit the milestone of giving three-quarters of adults a first COVID-19 vaccine dose and nearly half the population has received two doses of vaccine.

Britain has so far reported 904 cases of the Beta variant in total.

By contrast, in South Africa there is an average of 3,745 new cases each day, and only around 1 million out of a target of 40 million people have received a COVID-19 vaccine.

Hancock did not say if the vaccines under negotiation would be donated or kept for use domestically.

Earlier AstraZeneca Chief Executive Pascal Soriot said he was working with governments on increasing their pledged vaccine donations through the COVAX vaccine-sharing mechanism.

Hancock said AstraZeneca, which has pledged not to make a profit from vaccines during the pandemic, had released half a billion doses of the shot for global supply so far.

(Reporting by Alistair Smout in London, additional reporting by Olivia Kumwenda in Johannesburg; Editing by Aurora Ellis and Clelia Oziel)