Britain says new virus strain up to 70 per cent more transmissible

The new strain now accounts for more than 60 per cent of new infections in the capital, prompting alarm that it will quickly spread to less affected areas over the Christmas and New Year period.

Scottish First Minister Nicola Sturgeon responded to the announcement by closing the border to England.

When the science changes we must change our response and when the virus changes its method of attack we must change our method of defence.

UK Prime Minister Boris Johnson

The new level of restrictions for London and south east England are the toughest imposed in England since the first lockdown in March.

Prime Minister Boris Johnson – who last week resisted pleas to reverse his plan to loosen the rules so up to three households can mix at Christmas – said he had no choice but to act.

“When the science changes we must change our response and when the virus changes its method of attack we must change our method of defence,” he said.

Johnson only three days ago argued it would be “inhumane” for the government to cancel Christmas celebrations. The new winter lockdown is also at odds with his pledge in July that the country would return to “normality” by December 25.

The discovery of the mutated strain was announced on Monday but scientific analysis of its impacts were not concluded until Friday night UK-time.

Studies suggest the variant formed in September and accounted for 28 per cent of new infections in London by mid-November. That figure ballooned to 62 per cent by December 9.

“So what this tells us is that this new variant not only moves fast but it is becoming the dominant variant,” said chief medical officer Chris Whitty. “It is beating all the others in terms of transmission.”

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He said there was no evidence the strain makes people sicker but was less certain on the question of whether the new strain may be more resistant to vaccines.

“There are theoretical reasons to suspect some of the changes might alter some of the immune response but there’s nothing that’s been seen to suggest that’s the case,” he said.

“Our working assumption at the moment from all the scientists is that the vaccine response should be adequate for this virus. That needs to be looked at going forward and we need to be vigilant about this.”

Health authorities have notified the World Health Organisation about the strain and Johnson said Britain would be “totally transparent” with other countries. It is not known whether the variant might force some countries to consider closing their borders to the United Kingdom.

Chief scientific advisor Sir Patrick Vallance said viruses often mutated but this strain had gained force over autumn.

“We think it may be in other countries as well. We definitely think there’s a large outbreak in the UK,” he said.

“It may have started here, we don’t know for sure. There will be other types of mutations around the world.”

Professor Edmunds, a highly respected epidemiologist and member of the government’s powerful Scientific Advisory Group for Emergencies, told television station ITV the new strain was “the worst moment of the whole epidemic”.

“We will need much more severe measures to bring the incidence down,” he said.

“Worse than that, we are starting from a very high incidence already with hospitals stretched and NHS staff under strain. It is a very perilous situation.”

Responding to Edmund’s remarks, Whitty said: “Is this the worst moment? Well I’m afraid there have been so many terrible moments in this epidemic and this is another one.”

However, Whitty said while the virus was more transmissible, there were new medical countermeasures like a vaccine and treatments to make the situation better.

The new strain has the potential to increase the R – the reinfection rate which determines how many people one infected person passes the disease onto – by 0.4.

About 23,000 people have died since mid-September, bringing the official toll to 67,000.