The World Health Organisation urged rich countries on Friday to reconsider plans to vaccinate children and instead donate Covid-19 shots to the Covax scheme for poorer countries.
WHO chief Tedros Adhanom Ghebreyesus also said the second year of the pandemic was set to be more deadly than the first, with India a huge concern.
"In January, I spoke about the potential unfolding of a moral catastrophe," he told a press conference.
"Unfortunately, we're now witnessing this play out. In a handful of rich countries, which bought up the majority of the supply, lower-risk groups are now being vaccinated.
"I understand why some countries want to vaccinate their children and adolescents, but right now I urge them to reconsider and to instead donate vaccines to Covax.
"Because in low and lower-middle income countries, Covid-19 vaccine supply has not been enough to even immunise healthcare workers, and hospitals are being inundated with people that need lifesaving care urgently."
More than 160.71 million people have been reported to be infected by the virus globally and 3 477 379 have died, according to a Reuters tally.
Infections have been reported in more than 210 countries and territories since the first cases were identified in China in December 2019.