The UN health agency chief Tedros Adhanom Ghebreyesus Wednesday urged the advanced countries to suspend their ongoing or planned administration of third shots against Covid-19 until at least the end of the year to ensure vaccine supplies for developing countries. In early August, the World Health Organisation director-general had called for the suspension of the Covid-19 booster shots until the end of this month. But now he is seeking to extend the timeline for offering third shots, as the disparity in vaccine access for poorer countries has yet to be overcome. Read: US okays Covid booster dose for those with weak immune systems "A month ago, I called for a global moratorium on booster doses at least until the end of September, to prioritise vaccinating the most at-risk people around the world who are yet to receive their first dose," Tedros told a press conference. "Today I am calling for an extension of the moratorium until at least the end of the year, to enable every country to vaccinate at least 40 percent of its population," the WHO chief said. Some developed countries are moving ahead with booster shots to protect their populations amid recent surges in infections while developing countries have largely fallen behind in vaccination efforts against Covid-19. According to Tedros, while 5.5 billion doses of the Covid vaccine have been administered globally, 80% of them have gone to high and upper-middle-income countries. Read: What we know about Covid-19 booster shots Booster shots are meant to strengthen vaccine efficacy, but the WHO takes a position of not recommending them under the present circumstances, citing a lack of sufficient data on efficacy and potential side effects of the available Covid vaccines. The WHO chief also urged advanced countries to "fulfil their dose-sharing pledges" to developing countries by the end of September.