GENEVA, Oct 21 (Reuters) - The World Health Organization (WHO) on Thursday called on the world"s 20 richest nations, holding a summit next week, to step up donations of COVID-19 doses to the global south where vaccinations lag. "The @g20org countries must fulfil their dose-sharing commitments immediately," WHO director-general Tedros Adhanom Ghebreyesus told a news briefing. Gordon Brown, WHO ambassador for global health financing, said that if the world"s richest countries cannot mobilise for a vaccine airlift to developing countries, an epidemiological and economic "dereliction of duty will shame us all". There is still a shortfall of 500 million vaccine doses to reach WHO"s 40% vaccination target in all countries by year-end, while 240 million doses are lying unused in the West, Brown said. (This story corrects last paragraph to say 40% vaccination target is year-end, not mid-2022)