There will "never be zero risk" of catching Covid-19 and the possibility of another wave of infections cannot be ruled out, scientists have warned.
Dr Mike Tildesley, reader in infectious disease modelling at the University of Warwick, a member of the Government’s Scientific Pandemic Influenza Group on Modelling (Spi-M), said any form of reopening "could lead to higher risk".
He added people can minimise their risk if they follow guidelines, including mask wearing and social distancing.
England lifted more lockdown measures on Monday with shops, hairdressers and personal beauty services reopen.
The government has urged people to be cautious and ministers have warned the current wave of infections hitting mainland Europe could reach Britain.
Another expert also warned on Monday the UK's high vaccine numbers may not rule out another wave of the virus and pointed to Chile, which has high numbers of inoculation but is currently seeing a spike in infections.
When asked what the effect of reopening may have on infection rates, Dr Tildesley told Times Radio: "It’s hard to tell categorically but I think we do need to remember that with any form of reopening there’s going to be more mixing, and so we might expect that that could lead to higher risk.
"This is exactly why this road map has got five weeks in between the next couple of relaxations – it gives us enough time to monitor what happens if we do start to see a concerning rise in cases, and more importantly if we see a concerning rise in hospital admissions and people sadly dying from the disease.
He said "all the signs are pretty good at the moment" but could not rule out a resurgence of the virus and emphasised people had to follow the rules.
He added: “We should never say there can’t be any transmission if we follow those rules, what we’re doing is we’re trying to minimise the risk of transmission as much as possible.
“By taking these precautions there is never going to be zero risk, there’s always the possibility that even with those precautions you could get infected but you’re minimising your own risk of being infected and also potentially passing the virus on.”
Meanwhile, Sir David King, former chief scientific adviser to the Government, raised concerns about a third wave of infections in Chile.
He told Sky News: "Chile is a country where the rate of vaccination amongst the population was third highest in the world – they were ahead of us in terms of the number of people who have had the vaccine – and they’re suddenly now into a third wave.
"They now have 7,600 cases a day and the total number of people in Chile now who have Covid-19 is over a million.
"So what has happened in Chile is very, very surprising – a high percentage of people have been vaccinated, but here’s a variant of the disease coming through the country.”
Sir David said he did not think it would be possible to stop the "Brazilian variant" of coronavirus coming to the UK, but added that travel abroad was still possible "on a very restricted basis".
He said he supported a traffic light system for foreign travel, adding: "So if we’re talking about travelling directly to a country with a very low rate of the disease, and if the proper precautions are taken in that you’re fully tested or fully vaccinated, then I think it is quite feasible to allow people to travel overseas.
"But I think it should be on a very restricted basis."
Sir David was also critical of the Test and Trace system.
"It is spending £135 billion on private sector companies of our money, public money, on this process, and it hasn’t succeeded.
"If we have a new outbreak, we need to separate everyone with the disease, and those who have been in contact with them, from the rest of the population, and then we can go on with our business.”
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