Herd immunity in the UK is unlikely to be achieved until summer despite the possibility of another Covid-19 vaccine being approved, a scientist advising the government has said.

Calum Semple, professor of outbreak medicine at the University of Liverpool and a member of the Scientific Advisory Group for Emergencies (Sage), said the Oxford/AstraZeneca vaccine is a “game changer” if it is approved in the coming days as expected.

But he told BBC Breakfast: “To get the wider community herd immunity from vaccination rather than through natural infection will take probably 70% to 80% of the population to be vaccinated, and that, I’m afraid, is going to take us right into the summer I expect.”

It comes as hospitals in the South face a rise in pressure as the number of coronavirus patients receiving treatment heads towards the April peak, PA Media reports.

Paramedics in the capital are receiving almost 8,000 callouts daily, and Boxing Day was described as one of London Ambulance Service’s “busiest ever days”.

The 7,918 calls received by London Ambulance Service (LAS) on December 26 was up more than 2,500 on the 5,217 received on the same day last year, and medics are receiving support from other ambulance services in the South.

Dr Katherine Henderson, the president of the Royal College of Emergency Medicine, described her experience of working in a hospital on Christmas Day as one of “wall to wall Covid”.

“We see patients who are coming in who have Covid symptoms and then we have other people coming in with other symptoms who turn out to be Covid positive.

“Between that, there’s a great deal of difficulty getting those patients through into the wards,” she told BBC Breakfast.

“The chances are that we will cope but we cope at a cost – the cost is not doing what we had hoped, which is being able to keep non-Covid activities going.

“So we will stretch staff, the problem is at the moment we have a lot of staff sickness.”