A top scientist today warned that vaccines are not enough on their own to keep Covid infections under control as pressure mounts on Boris Johnson to bring in new measures.
Professor Adam Finn, who is on the Joint Committee of Vaccination and Immunisation (JCVI), said the NHS is already under "enormous pressure".
Prof Finn said that although vaccines are effective in preventing serious illness, they are not able to stop coronavirus spreading altogether, despite reducing cases.
This heightens the risk of the virus reaching those most at risk, including those who are unvaccinated, he said.
So far the government has resisted calls to switch to its "Plan B", which would see a return to mandatory mask wearing, working from home and the introduction of vaccine passports.
More than 333,000 people have tested positive for the virus in the past seven days, while 934 lives have been lost to Covid, Department of Health figures show.
Prof Finn told Trevor Phillips on Sky News: "I think that the vaccine programme is doing a lot to make the situation much less severe than it would otherwise be.
"And the vaccines principally are very effective at stopping people from getting seriously ill.
"They're not so effective unfortunately at stopping infections altogether or stopping the virus from being spread about.
"They do have an effect on that, but they're not by themselves going to be enough at the present time to keep the spread of the virus under control.
"And we do need to see people continuing to make efforts to avoid contact, to avoid transmission, and to do other things as well as get vaccinated if we're going to stop this rise from going up further."
Prof Finn warned against complacency in what he said is a "worsening" situation.
"And they will go up as the number of cases go up because the virus will reach people who are vulnerable and who may get seriously ill," he told Trevor Phillips On Sunday on Sky News.
"So I think we can't be complacent about this. This is a worsening situation in an NHS which is already under enormous pressure."
Prof Finn said the biggest risk is amongst those who have not had any vaccine yet, including younger adults.
"Many of the hospitalised people we're seeing at the moment are in fact unimmunised people," he said.
Prof Finn said vaccines are not going to be enough to keep the spread of coronavirus under control, and said people need to make effort to avoid contact in order to slow transmission rates.
Prof Finn said it is important to "stick to the science" when discussing the prospect of extending the Covid-19 booster programme to people under 50 and offering booster jabs at five months rather than six months.
He said: "Just giving more people vaccines, including people who maybe don't actually need the vaccines yet, could actually run the risk of making things worse rather than better.
"If you boost people before they actually need the vaccine, it is in some senses a waste of vaccine, but also it means that you are immunising them earlier and they may make a smaller response to the vaccine and that response may wear off earlier.
"So I think the idea of just getting more doses indiscriminately into people's arms is not really necessarily going to solve the problem.
"I think we do need to focus particularly on the most elderly people and do this in a structured and strategic way in order to have the maximum impact."
Dr Katherine Henderson, president of the Royal College of Emergency Medicine, said emergency departments are in a "terrible place".
Asked if she thinks emergency departments are going to be able to cope this winter, she told Sky News's Trevor Phillips On Sunday:
"We're already struggling to cope. This is not something that's coming in the next couple of months. We're already in a terrible place where we have got large queues of ambulances with vulnerable people waiting in those ambulances to be offloaded into departments and other patients at home waiting to be picked up by the ambulance.
"That's the thing that really worries me; that these are patients who have not yet received treatment that we don't necessarily know what's wrong with them that we're really struggling to get into our healthcare facilities to then work out what we need to do.
"That's the real worry from my point of view and we're already in that situation."
But the government continues to resist the growing calls to take more serious measures to tackle the virus resurgence.
Asked if it is time to bring in Plan B to tackle coronavirus, Chancellor Rishi Sunak said "at the moment the data does not suggest that we should be immediately moving to Plan B".
He told BBC One's The Andrew Marr Show: "Well, the Prime Minister actually just said that we're looking at the data all the time, as you would expect us to.
"We're monitoring everything, but at the moment the data does not suggest that we should be immediately moving to Plan B, but of course we will keep an eye on that and the plans are ready."
Vaccines minister Maggie Throup said Plan A is "working" and "where we need to be".
Asked where case numbers will have to get to before the public will be asked to work from home, Ms Throup told LBC: "The public has been very patient in doing what we've asked them to do.
"And I think Plan A has actually opened up people's lives and that's so important because if we do need to take further measures I'm sure they'll have appreciated exactly the freedoms we've been able to offer them at this time.
"Plan A is working, as I said, the data right now shows that Plan A is working."Read More Read More