WHO director-general Tedros Adhanom Ghebreyesus said it was "shocking" how little had been done to avert an entirely predictable "catastrophic moral failure" to ensure the equitable distribution of vaccines worldwide.
The gap was "growing every single day, and becoming more grotesque every day," he told a press conference.
"Countries that are now vaccinating younger, healthy people at low risk of disease are doing so at the cost of the lives of health workers, older people and other at-risk groups in other countries," Tedros said. "The inequitable distribution of vaccines is not just a moral outrage. It's also economically and epidemiologically self-defeating."
He continued, "Some countries are racing to vaccinate their entire populations -- while other countries have nothing."
Tedros said rich countries were giving themselves a false sense of security. The UN health agency chief said the more transmission of the virus, the more variants are likely to emerge -- and the more of those that spring up, the more likely they are to evade vaccines.
Tedros said countries were in a race against time to bring down transmission and wealthy nations needed to match their promises of solidarity with action on getting vaccines to poorer nations.
"Unless we end this pandemic as soon as possible, it can keep us hostage for more years to come," he warned.
56 percent of the doses have been administered in high-income countries accounting for 16 percent of the global population. Just 0.1 percent have been administered in the 29 lowest-income countries, home to nine percent of the global population.
WHO emergencies director Michael Ryan said nations were grasping at straws, thinking that simply administering lots of vaccine doses would be a "golden solution" to end the crisis.
"I'm sorry: it's not," Ryan said. "The disease is on the march again in countries where we have an opening up, natural fatigue, low vaccination coverage, poor surveillance and control measures in place," he said, calling the combination "a recipe for larger outbreaks".
"I'm afraid we are investing way too much in this (vaccines) as the only solution to fix our problems," he said.