The head of the UN agency stressed that "hundreds of millions" worldwide are still waiting for their first dose.
The head of the World Health Organisation (WHO) called on Wednesday for a moratorium on booster doses of COVID-19 vaccines so that those vaccines can be made available to countries that have only been able to inoculate a small proportion of their population.
Dr. Tedros Adhanom Ghebreyesus told reporters that although "hundreds of millions of people are still waiting for their first dose, some rich countries are moving towards booster doses" — a dose to be administered after a full vaccination course.
Several countries including France, Germany, and Israel have started administering booster doses. Britain and the US are reportedly considering it as well.
"I understand the concern of all governments to protect their own people from the Delta variant. But we cannot accept countries that have already used most of the global supply of vaccines using even more of it, while the world's most vulnerable remain protected," he added.
Dr. Tedros also stressed that of the more than 4 billion doses of COVID-19 vaccines administered so far globally, more than 80% had gone to high- and upper-middle-income countries, which account for less than half of the global population.
According to WHO, high-income countries have now administered almost 100 doses for every 100 people, while low-income countries have only been able to administer 1.5 doses for every 100 people.
"We need an urgent reversal, from the majority of vaccines going to high-income countries, to the majority going to low-income countries," he said.
"Accordingly, WHO is calling for a moratorium on boosters until at least the end of September, to enable at least 10% of the population of every country to be vaccinated," he went on.
He highlighted that the world's 20 biggest economies — collectively known as the G20 — have a "vital leadership role to play, as the countries that are the biggest producers, the biggest consumers and the biggest donors of COVID-19 vaccines."
WHO officials say the science is unproven about whether giving booster shots to people who have already received two vaccine doses is effective in preventing the spread of the coronavirus.
The WHO has been denouncing the unequal distribution of vaccine doses for months, criticising for instance, countries that have moved to offer the vaccine to all children above the age of 12, when lower-income countries have struggled to immunise their health care professionals.
The UN agency in May set the target of inoculating 10% of the population in every country by the end of September. The WHO chief said Wednesday that "we're not on track" to reach the target.