England's unlocking plans will proceed on July 19 despite threat of virus variants

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Prime Minister Boris Johnson announced Monday that step four in the government's road map out of lockdown would go ahead as planned on July 19 but cautioned Britons that it was “absolutely vital we proceed with caution”.

The UK leader said quarantine for those from Red List countries would continue, isolation rules would remain for a time and that it was not a matter of “simply reverting instantly to life as it was before”.

"I cannot say this powerfully or emphatically enough, this pandemic is not over," he said.

"To take these steps we must be cautious and must be vaccinated."

Mr Johnson highlighted the most important issue was UK residents continued to get vaccinated as scientists have warned England’s plans to fully reopen next week is at risk from mutations of the virus.

The change in rules will mark the end of all coronavirus regulations meaning the number of people gathering will no longer be limited, while mandatory social distancing and mark-wearing will come to an end.

"Cases will rise as we unlock, so as we confirm our plans today, our message will be clear. Caution is absolutely vital, and we must all take responsibility so we don’t undo our progress," added Mr Johnson.

He emphasised the need for "personal responsibility". In that regard, the public will still be “expected” to wear masks and urged to work from home after July 1 even if work from home guidance is due to formally end.

Health minister Sajid Javid on Monday said plans to relax restrictions would go ahead.

But he also urged people to act responsibly because the link between cases and deaths while "severely weakened" had yet to be fully broken.

"We firmly believe that this is the right time to get our nation closer to normal life, so we will move to the next stage of our roadmap on July the 19th," Mr Javid told parliament.

“To those who say ‘why take this step now’ I say ‘if not now, when? There will never be a perfect time to take this step because we simply cannot eradicate this virus.”

The UK has recorded a sharp rise in cases in recent weeks, with 31,772 positive tests reported on Sunday.

Peter Openshaw, professor of experimental medicine at Imperial College London, said the rise in cases was leading to increased hospital admissions and deaths.

“It’s beginning to feed into a quite concerning doubling of the rate of hospital admission,” he told the BBC.

“If we look at hospital admissions, they are up almost 60 per cent. If we look at deaths, although relatively small, they are up 66 per cent on the week before.

"We know there’s a time lag built into the epidemiology and built into all the observations we have. We’re all very concerned about where this is going to go over the next month or so.”

The co-founder of BioNTech, the company which manufactured one of the most used Covid-19 vaccine alongside Pfizer, fears that vaccination obligation will produce the "opposite effect" of that sought.

Ugur Sahin said vaccination was an “individual responsibility” and advocated an approach based on transparency and education rather than obligation.

He also said the rise of the Delta variant and other Covid strains were of particular concern and told Reuters that unvaccinated people would "most likely be infected " with the virus, which he said was becoming increasingly contagious.

"The next generation of the virus will have an infectivity rate of around 6 to 8, which means that an infected person can infect up to 8 people who are not immune," he said.

Heath Secretary Sajid Javid previously said infections could reach 100,000 per day later in the summer, but Mr Johnson is hopeful the country’s vaccination drive will provide enough protection even if the number of Covid cases rises substantially.

About 87 per cent of adults in the UK have received a first dose of a Covid-19 vaccine, while 66 per cent are fully vaccinated.

A WHO epidemiologist said she had been devastated to watch unmasked crowds singing and shouting at the Euro 2020 soccer final in London on Sunday, expressing concerns that it would spur COVID-19 transmission, including of the Delta variant.

In unusually forthright comments from the U.N. health agency, which usually refrains from remarking on the policies of individual member states, its COVID-19 technical lead Maria Van Kerkhove called the sight of the more than 60,000 spectators at the match between Italy and England "devastating".

"Am I supposed to be enjoying watching transmission happening in front of my eyes?" she tweeted in the late stages of the match.

"The #COVID19 pandemic is not taking a break tonight ... #SARSCoV2 #DeltaVariant will take advantage of unvaccinated people, in crowded settings, unmasked, screaming/shouting/singing. Devastating."

Dr Mike Tildesley, an expert in infectious disease modelling who advises the government, said more mutations of the virus were likely.

“We need to be careful. We can’t just say once we’ve broken the link between cases and hospital admissions that we are pretty much safe and no one gets really sick so it’s fine to have a big wave of cases,” he told Times Radio.

“Of course the more cases you have, particularly with high levels of vaccine protection, that does then kind of challenge the virus a little bit more and gives more potential for it to mutate into a form where the vaccines are less effective.”

He criticised the government for "mixed messaging" on the wearing of face masks.

Vaccines Minister Nadhim Zahawi said at the weekend people would still be “expected” to wear face coverings in enclosed indoor spaces, but other ministers said they plan to stop wearing masks as soon as legally possible.

"I think it's actually quite confusing for people to know what the right thing to do is,” Dr Tildesley said.

“I think all we can do is take a sort of appropriate approach where we look at the situation and weigh up risk ourselves and I hope enough people do that going forward and we don't see a big surge."

Prof Adam Finn from the University of Bristol, who sits on the Joint Committee for Vaccination and Immunisation, said it would be helpful if some social distancing regulations remained in place.

“Vaccination is not a really good tool for dealing with the fire in the house once the fire is really going,” he said.

“It’s much better at stopping the house being flammable in the first place.”

Health Minister Edward Argar said there would still be "clear and strong guidance" from the government.

“We would urge caution and the innate common sense of the British people around things like mask-wearing," he told Sky News.

"We're in a position now where the vaccination programme – our defensive wall against this virus – is proving hugely effective."