Humanity is not losing the war against the Covid-19 pandemic and will eventually conquer the virus, the World Health Organization said Wednesday.

As daily global deaths from the disease topped 18,000 for the first time and with new variants spreading rapidly around the globe, Maria Van Kerkhove, the WHO's technical lead on Covid-19, said the mutations did not imply defeat.

"Does it mean we're losing this war? No," she told a WHO live social media event.

"We are in the fight of our lives. We have to make sure that we're not fighting each other; that we're fighting the virus... the variants included.

"We can conquer this virus -- and we will conquer this virus."

In the global scramble for vaccine doses, wealthier nations are pressing ahead with immunising the elderly and medical staff while poorer countries wait for their very first batches.

Michael Ryan, the WHO's emergencies director, said it would unacceptable for rich countries to move on and start vaccinating their general population while health workers and extremely vulnerable communities elsewhere remained exposed.

"We simply cannot have a situation where front-line workers, health workers risking their lives every day, and the most vulnerable people, are not accessing vaccines," he said.

"If we reach a situation in the developed world where perfectly healthy people are being vaccinated and those front-line workers and vulnerable people are not, it is simply not fair.

"Let's share that now, to be sure that those most at risk, the bravest, the most courageous of us all, get covered and get protected, and those who are most likely to suffer and die.

"And in doing that, we'll end the problem quicker. So it's not only good: it's smart."