The vast majority of COVID-19 vaccines administered have so far gone to wealthy nations, the World Health Organization (WHO) reported.

Although more than 700 million vaccine doses have been administered globally, richer countries have received more than 87 percent, and low-income countries just 0.2 percent.

"There remains a shocking imbalance in the global distribution of vaccines", said WHO chief Tedros Adhanonom Ghebreyesus, speaking during the agency's regular briefing from Geneva.

"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."

The global solidarity initiative, COVAX, has also experienced a shortage of vaccines. While the mechanism has distributed some 38 million doses so far, it was expected to deliver nearly 100 million by the end of March.

"The problem is not getting vaccines out of COVAX; the problem is getting them in", he said.

"We understand 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."

COVAX partners, who include Gavi, the vaccine alliance, are working on several options to scale up production to meet the goal of delivering two billion doses by the end of the year.

Dr. Seth Berkley, the Chief Executive Officer at Gavi, highlighted the need for continued solidarity.

"What we are now beginning to see are supply constraints, not just of vaccines, but also of the goods that go into making vaccines", he said.

COVAX is in discussions with several high-income countries to get them to share surplus vaccine doses, he said. It is also developing cost-sharing mechanisms so that low income countries can buy additional doses through COVAX, funded by multilateral development banks.

Dr. Berkley added that financing is also needed as demand for vaccines has risen with the emergence of new COVID-19 variants.