A new coronavirus variant first detected in South Africa has been identified in the UK, as scientists warned of the risks posed by the growing number of Covid-19 mutations.

Two cases of the 501.V2 strain, which has caused a recent surge of Covid-19 infections in South Africa, have been identified in contacts of people who had arrived from the country in the past fortnight, Matt Hancock, UK health secretary, said on Wednesday.

“This virus is yet more transmissible and appears to have mutated further than the new [strain detected in the UK]”, Mr Hancock said, adding that the travellers and their close contacts must quarantine immediately.

The variant first detected in South Africa emerged independently from its counterpart in the UK, B.1.1.7, which has driven a rapid increase in Covid-19 cases across London and south-east England.

Genetic analysis shows that the variants detected in the UK and South Africa both have more than 20 mutations — an unusually large number of changes to the virus. Some of the mutations differ between the two strains, though some of the changes are the same.

Both variants include changes to the spike protein, which the coronavirus uses to gain entry to human cells. Scientists in South Africa have said it is “very plausible” that this N501 spike mutation may make it more infectious — perhaps because it produces a higher “viral load” in the upper respiratory tract. But they have cautioned that more study is needed.

“The preliminary data suggests that the virus that is now dominating in the second wave is spreading faster than the first wave,” said Salim Abdool Karim, the South African government’s leading Covid-19 adviser. “It is not clear if the second wave has more or less deaths, in other words, the severity is still very unclear.”

Scientists in South Africa, like their UK counterparts, are looking for evidence to show whether the new variant is likely to cause different symptoms and whether it would be harder to detect, treat or vaccinate against.

The Africa Centres for Disease Control and Prevention held an emergency meeting on Monday to discuss the 501.V2 variant, which emerged in Nelson Mandela Bay in Eastern Cape, in the south of the country. It concluded that there was no immediate need to restrict trade or travel across the continent, largely because the majority of African countries already require a negative Covid-19 test before entry.

The emergence of the new variant has coincided with what the Africa CDC called a second wave of Covid-19 in Africa, in which the number of infections and deaths has risen in some countries. It urged countries to step up testing and tracing as well as genomic sequencing to pick up the prevalence of the new strain or strains.

Like the UK — but unlike most other countries — South Africa makes an effort to track mutations of the virus through extensive genomic sequencing. British and South African scientists have suggested that this surveillance might be one reason why they have detected significant new strains that have not yet been documented in other countries.

“We are entering a particularly dangerous phase of this pandemic,” said Dr Andrew Preston, a microbiologist at the University of Bath. The evolution of two new variants at about the same time with an unusual large number of mutations makes “the effective rollout of the vaccines even more time-critical,” he said.