Have your say: How concerned are you about a fourth COVID wave?

As coronavirus cases rise again across the UK, experts have warned that a fourth wave of infections this winter should be planned for.

Despite previously assuring the public that no further lockdowns would be imposed on the country, Boris Johnson admitted on Monday that they may be needed if infection numbers threaten to overwhelm health services.

The prime minister warned that the UK faces a "rough winter" but reassured reporters that it is “looking good” for 19 July to be the “terminus point” to England’s coronavirus restrictions.

Infection numbers have increased in recent weeks due to the highly transmissible Delta variant, first identified in India, which now accounts for 99% of new coronavirus infections in the UK.

He said: “You can never exclude that there will be some new disease, some new horror that we simply haven't budgeted for or accounted for.

"Obviously there are big pressures on the NHS, which is all the more reason to reduce the number of COVID cases now, give the NHS the breathing space it needs to get on with dealing with all those other pressures."

The NHS has warned hospitals they could face a fourth wave with half the number of patients as the first wave in spring last year, according to the Health Service Journal.

But NHS England has also told them to carry on with 80% of normal elective activity should the fourth wave occur.

Johnson's remarks came as Professor Calum Semple, member of the Scientific Advisory Group for Emergencies (Sage), which advises the government, said that children and elderly people will be particularly vulnerable to endemic viruses towards the end of the year.

With social distancing having reduced exposure to the usual endemic respiratory viruses that circulate he warned there could be a rise in bronchiolitis and a rise in community-acquired pneumonia in children and the elderly.

Professor Semple called it the "fourth wave winter" but added it would be much milder than the previous ones.

Semple told Times Radio: “I suspect we’ll have a pretty miserable winter because the other respiratory viruses are going to come back and bite us quite hard. But after that, I think we’ll be seeing business as normal next year."

Government adviser Dr Susan Hopkins also warned at the weekend that there may be the need for winter lockdowns if hospitals become "overwhelmed".

Read more: What you can and can't do under current lockdown rules

She told the BBC’s The Andrew Marr Show: “We may have to do further lockdowns this winter, I can’t predict the future, it really depends on whether the hospitals start to become overwhelmed at some point.

“But I think we will have alternative ways to manage this, through vaccination, through antivirals, through drugs, through testing that we didn’t have last winter."

However, not all experts support the idea of lockdowns to control the virus.

Professor Devi Sridhar, chair of global public health at Edinburgh University Medical School, tweeted: “Another lockdown in winter would be unthinkable. We must get things in order now instead of accepting rises in hospitalizations & then lockdown as inevitable.

“The harms of lockdown are huge and we now have vaccines, testing, and isolation measures to avoid blanket restrictions.”

Watch: Are hospitalisations coming down? Cautious optimism with COVID deaths remaining low despite rising number of cases