As Covid-19 cases balloon again in Europe, the World Health Organization called Friday for more targeted vaccination efforts to ensure the most vulnerable worldwide get the jabs.

The UN health agency said Europe, once again at the epicentre of the pandemic, registered nearly two million Covid cases last week.

That is "the most in a single week in the region since the pandemic started," WHO chief Tedros Adhanom Ghebreyesus told reporters.

But as countries scramble to rein in transmission by reimposing restrictions or rolling out more vaccines and boosters, WHO said it was vital to ensure the jabs were going to those who needed them most, on the continent and beyond.

"It is not just about how many people are vaccinated. It is about who is vaccinated," Tedros said.

"It makes no sense to give boosters to healthy adults, or to vaccinate children, when health workers, older people and other high-risk groups around the world are still waiting for their first dose," he said.

More and more countries have been rolling out additional doses for their already vaccinated populations, despite repeated calls from the WHO for a moratorium on boosters until the end of the year to free up jabs for poorer nations.

"Every day, there are six times more boosters administered globally than primary doses in low-income countries," Tedros said, insisting that "this is a scandal that must stop now."

More targeted efforts were also needed within the wealthy countries that have access to enough doses, but where many refuse to get the jabs, WHO emergencies director Michael Ryan said.

He pointed out that in nations with broad and high vaccination coverage, increasing Covid cases will not translate into many more hospitalisations and deaths, since the jabs are very effective at protecting against severe illness.

But he warned that even in countries where overall vaccination numbers are high, health systems could quickly come under pressure if significant pockets of vulnerable populations remained unvaccinated.

"If you're in Europe right now, where we've got that intense transmission, and you're in a high risk of vulnerable group or an older person and you're not vaccinated, your best bet is to get vaccinated," he told reporters.

He pointed to a recent British study that showed a non-vaccinated person has a 32-fold greater risk of dying in this pandemic than a vaccinated person.

"That's very good odds if you want to look at that in terms of something that enhances your chance of life."