As concerns rise over the new B.1.1.529 variant, the UK will impose a travel ban against six African nations to guard against a new Covid-19 variant dubbed “the worst one we’ve seen so far”.

UK officials sounded the alarm on Thursday night over the B.1.1.529 variant, which has the potential to evade immunity built up by vaccination or prior infection.

Health Secretary Sajid Javid said the new variant identified in South Africa “may be more transmissible” than the Delta strain and “the vaccines that we currently have may be less effective”.

He said that flights to England from South Africa, Namibia, Lesotho, Botswana, Eswatini and Zimbabwe will be suspended from midday on Friday and all six countries will be added to the red list.

While no cases have been found in Britain, officials raised concern over a rapid rise in cases in South Africa.

Anyone who has arrived from the country in the last 10 days will be invited to come forward and take a test by the UK Health Security Agency.

The UK Government said on Thursday that UK and Irish residents who arrive in England between midday on Friday and 4am on Sunday, and who have been in the six countries within the last 10 days, must quarantine at home for 10 days and take NHS PCR tests on day two and day eight, even if they already have a lateral flow test booked.

Passengers – including UK and Irish residents – arriving from 4am on Sunday will be required to book and pay for a Government-approved hotel and quarantine for 10 days. They must also take tests on day two and day eight.

    Direct flights from the six nations to the UK are being temporarily banned until 4am on Sunday, once the quarantine hotels have been set up. 

The Scottish Government also confirmed all arrivals from the six countries will be required to self-isolate and take two PCR tests from midday on Friday, while anyone arriving after 4am on Saturday will need to stay at a managed quarantine hotel.

The Northern Ireland Executive announced it was following England with the same restrictions.

At the moment, around 500 to 700 people are travelling to the UK from South Africa each day, but it is expected this figure could increase as the festive period begins.

From midday on Friday November 26, non-UK and Irish residents who have visited the nations in the previous 10 days will be refused entry into England. 

Asked what the situation would mean for the UK over the coming weeks, Mr Javid said: “We’ve got plans in place, as people know, for the spread of this infection here in the UK and we have contingency plans – the so-called Plan B.

“But today’s announcement, this is about a new variant from South Africa – it’s been detected in South Africa and Botswana – and this is about being cautious and taking action and trying to protect, as best we can, our borders.”

The variant has been classed as a “variant under investigation” in the UK, with one senior UK Health Security Agency (UKHSA) expert describing it as “the worst variant we have seen so far”.

Only 59 confirmed cases have been identified – three were in Botswana, two were in Hong Kong among people who had travelled from South Africa, and the remaining were confirmed in South Africa.

The variant has more than 30 mutations – around twice as many as the Delta variant – which could potentially make it more transmissible and evade the protection given by prior infection or vaccination.

Experts from the UKHSA have been advising ministers on the issue.

A number of scientists have expressed serious concern over the variant due to the significant number of mutations in the spike protein.

One senior scientist said: “One of our major worries is this virus spike protein is so dramatically different to the virus spike that was in the original Wuhan strain, and therefore in our vaccines, that it has a great cause of concern.”

Experts from the World Health Organisation (WHO) are meeting with South African officials on Friday to assess the evolving situation in the country.

The variant could eventually be given the moniker “Nu” – with the most concerning variants given named after the Greek alphabet.

UK officials were said to be “very worried” after they examined details on the variant on the international database – and have taken significant steps just three days after the details were uploaded.

The variant is a “dramatic change” from anything seen previously by UK scientists.

It has mutations which have been observed in other variants, but also ones that scientists have not yet seen.

As such, they think that if a new vaccine were needed to combat the variant, it could take some time.

But officials do not yet have enough evidence to call it a “variant of concern”.

As of yet there is not good evidence on transmissibility or the impact on vaccine effectiveness, and there is also no evidence on whether or not it causes more severe disease.

The risk of reinfection is not known, but it is expected a picture on this will develop quickly – this would be the first signal the variant could evade the body’s defences.

Experts have predicted “some reduced vaccine effect” but are not able to judge how bad it could be.

Some compared it to the Beta variant – which saw vaccine efficacy reduced by 30%-40%.

While there have been no cases seen in the UK yet, it is always possible that a case could have slipped in – but officials think that the likelihood of cases remains “low”.

Health officials said that Covid-19 booster jabs have become “particularly critical” given the development.