Johnson slams anti-vaxxers' 'mumbo jumbo'

British prime minister Boris Johnson on Thursday hit out at anti-vaccine campaigners' "mumbo jumbo" and "nonsense" in his toughest attack yet on those opposed to Covid-19 jabs.

"I want to say to the anti-vax campaigners, the people who are putting this mumbo jumbo on social media: they are completely wrong," Johnson told journalists.

"You haven't heard me say that before, because I think it's important we have a voluntary approach in this country and we're going to keep a voluntary approach," he said, during a visit to a vaccination centre.

The UK, already among the European countries worst hit by the pandemic, with a virus death toll of nearly 150,000, has seen a fresh surge in cases due to the arrival of the Omicron variant in late November.

Johnson noted that other European countries were going for "coercion", after Italy on Wednesday made Covid-19 vaccinations mandatory for all those aged over 50, with fines for those who refuse.

"What a tragedy that we've got all this pressure on the NHS (National Health Service), all the difficulties that our doctors and nurses are experiencing and we've got people out there spouting complete nonsense about vaccination," he added.

"It's absolutely wrong, it's totally counterproductive, and the stuff they're putting out on social media is complete mumbo jumbo."

Johnson said Tuesday it was "absolutely crazy" that intensive care units in Britain were being filled by the unvaccinated, pushing stretched NHS resources to the limit.

He noted the country had two million vacant vaccination slots this week and that the majority of people getting intensive hospital care for Covid are not fully jabbed.

England's chief medical officer Chris Whitty added at the time he was "saddened" by the number of unvaccinated patients in hospital and "frustrated" at the deliberate scare tactics of anti-vaxxers.