Tedros, during a briefing on Friday, said that out of 220 countries and economies, 194 have now started vaccination, and 26 have not. Of those, 7 have received vaccines and could start and further 5 countries should receive their vaccines in the coming days.

"That leaves 14 countries who have not yet begun vaccination, for a range of reasons. Some have not requested vaccines through COVAX, some are not yet ready, and some plan to start in the coming weeks and months," he said.

The chief further said that COVAX has delivered more than 38 million doses of vaccine to more than 100 countries and economies in the past six weeks.

"We're encouraged that almost all countries who want to start have now started. However, I emphasize the word start. Most countries do not have anywhere near enough vaccines to cover all health workers, or all at-risk groups, never mind the rest of their populations. There remains a shocking imbalance in the global distribution of vaccines," he said.

"On average in high-income countries, almost one in four people has received a vaccine. In low-income countries, it's one in more than 500. Let me repeat that: one in four versus one in 500. COVAX had been expecting to distribute almost 100 million doses by the end of March, but due to a marked reduction in supply, we have only been able to distribute 38 million doses," the WHO chief pointed out.

"We hope to be able to catch up during April and May," he said.

Tedros said that it was understandable that some countries and companies plan to do their own bilateral vaccine donations, bypassing COVAX for their own political or commercial reasons.

"These bilateral arrangements run the risk of fanning the flames of vaccine inequity. This is a time for partnership, not patronage. Scarcity of supply is driving vaccine nationalism and vaccine diplomacy," he said.

According to The Hill citing media reports, additional delays have occurred because the COVAX program relied heavily on the AstraZeneca vaccine that is being hit with safety concerns over the formation of rare blood clots in some who have received that vaccine.

US Treasury Secretary Janet Yellen recently called on rich countries to donate more vaccine doses to poorer nations saying the poorer nations will face a "profound economic tragedy" without the help.

The Hill further reported that Tedros has previously asked richer countries to donate 10 million vaccine doses to the COVAX program for developing countries, but the calls have largely gone unanswered.

Many countries in the European Union have been hit by a slow vaccination rollout.

Washington has said they are focusing on vaccinating all of its citizens first then ensuring that neighbouring countries Canada and Mexico are vaccinated.