Virologist from the University of Nottingham Professor Jonathan Bell said the rise in JN.1 cases is a “sign of things to come” however downplayed the risks.

He said: “New variants will continue to evolve, replace pre-existing variants causing major outbreaks of infection.

“I don’t think this [particular] rise is too concerning.

“We know that in the majority of people vaccines continue to protect against serious disease, that’s why it’s important for vulnerable people to ensure that they’ve had their latest vaccine booster jab.”

By the end of December 13, 3,854,999 people had been given a spring booster.

Although JN.1 is believed to be more infectious than the other Covid sub-variants circulating in the UK at the moment, there is nothing to suggest it causes more severe disease.

However, emerging anecdotal evidence suggests the new bug could be making people more unwell due to waning immunity.

Prof Openshaw added: “It’s a surprisingly devious virus, sometimes making people quite ill and occasionally leading to having ‘long Covid’.”