Highly contagious new variants of coronavirus will emerge more frequently and spur further infection waves such as those threatening to overwhelm hospitals in the UK and South Africa, one of the world’s leading infectious disease experts has warned.

Salim Abdool Karim, chairman of South Africa’s Covid-19 ministerial advisory committee, also said it was too early to know the extent to which existing vaccines would provide immunity to the new variants.

Scientists around the world have been alarmed by the rapid spread of the new 501.v2 variant first detected in South Africa and the equally infectious B.1.1.7 variant that has led to a recent surge in cases in the UK. Other variants have emerged recently in Brazil and Japan.

Prof Abdool Karim, the epidemiologist who led South Africa’s fight against HIV/Aids, explained that viruses evolved as they infected people with partial immunity in order to escape recognition by their antibodies.

“We’re going to see this occur more commonly now than in 2020, as we vaccinate and as more people are infected,” he said in an interview with the Financial Times.

The epidemiological finding of increased transmissibility was supported by “biological evidence showing the 501.v2 variant binds more readily and more strongly to human cells”, added Prof Abdool Karim.

Line chart showing new confirmed cases of Covid-19 per 100,000 people in UK, South Africa, Brazil and Japan since November 1

The Sars-Cov-2 virus that causes Covid-19 has mutated once or twice a month on average since appearing in humans in late 2019. But the variants detected in South Africa and the UK carry about 20 mutations, where previous ones had been associated with one or two significant genetic changes.

Greater numbers of mutations can cause the behaviour of the virus to change more extensively. The variants that originated in the UK and South Africa are both about 50 per cent more infectious than previous forms of the virus, although neither is thought to cause more severe symptoms.

Another question is how the variants interact with the human immune system, in particular whether they reduce the effectiveness of Covid-19 vaccines. “We’ll have an answer within the next two weeks or so but we don’t know yet,” Prof Abdool Karim said of the 501.v2 variant.

Antibodies from people who have recovered from Covid-19 were less effective against the new variant, Prof Abdool Karim said, but “the way in which T-cells and the B-cells function is quite different in vaccine immunity. I wouldn’t extrapolate from natural immunity to vaccine immunity.”

Less is known about the new variant of Sars-Cov-2 detected in Brazil after scientists sequenced 180 viral genomes from the state of Rio de Janeiro.

Researchers from Brazil’s national genomic surveillance network identified a “significant increase” in cases of the variant that “raise concerns about public health management” in a country with more than 200,000 Covid-19 deaths, the second-highest number of fatalities after the US.

Carolina Voloch of the Federal University of Rio de Janeiro, lead author of a preprint paper about the variant, said that samples taken from Rio state showed it increased in frequency from zero in September to 20 per cent by November.

“For now we can’t say it’s more contagious. What we can say is there’s an increase in the frequency of this lineage,” said Dr Voloch.

Japanese authorities also detected a new variant in four passengers who arrived from Brazil on January 2. It is related to the B.1.1.248 variant of the virus circulating in Brazil, and shares some of the same mutations as the UK and South African variants, according to Japan’s National Institute of Infectious Diseases.

But Emma Hodcroft, a viral geneticist at the University of Bern who monitors the evolution of Sars-Cov-2, said: “It doesn’t look as though these four cases from Japan are part of the larger Brazilian cluster.”

She agreed that conditions in 2021 were likely to favour the evolution of more variants with multiple mutations, as a larger proportion of people were infected and evolutionary pressure on the virus increased.

A modelling study by scientists at Emory and Penn State, published in Science journal on Tuesday, suggested the evolutionary path for Sars-Cov-2 would eventually lead to a less virulent “endemic” virus, joining the ranks of other mild cold-causing coronaviruses that currently circulate in humans.

“We’re in uncharted territory but . . . immunological indicators suggest that fatality rates and the critical need for broad-scale vaccination may wane in the near term, so maximum effort should be on weathering this pandemic,” said Ottar Bjornstad, a Penn State professor.

Prof Abdool Karim also made the point that the selective pressure for all viruses was to “become more transmissible and less pathogenic over time”.

Additional reporting: Robin Harding in Tokyo and Carolina Pulice in São Paulo