Recent studies of the Pfizer/BioNTech vaccine showed it produced far fewer neutralising antibodies against Omicron than against the original strain, but that this deficit could be reversed by a third, booster, jab.
Dr Tedros said boosters could play an important role in curbing the spread of Covid-19, but that it was “a question of prioritisation”.
“The order matters. Giving boosters to groups at low risk of severe disease or death simply endangers the lives of those at high risk who are still waiting for their primary doses because of supply constraints,” he said.
Supplies to the global vaccine-sharing programme Covax have increased in recent months.
However, world health officials fear a shortfall of tens of millions of doses – like the one which occurred in the middle of this year when India suspended its vaccine exports – could happen again.
In poorer countries, some vulnerable people are yet to receive a single dose.