Health officials and experts in Asia have welcomed US plans to share 500 million more doses of the Pfizer vaccine with the developing world, but some say it would take more than donations alone to address huge vaccination gaps that threaten to prolong the pandemic.

President Joe Biden was set to make the announcement on Thursday in a speech before the start of the Group of Seven summit in Britain. Two hundred million doses – enough to fully protect 100 million people – would be shared this year, with the balance to be donated in the first half of 2022, according to a source familiar with the matter who confirmed the news of the Pfizer sharing plan.