Scientists say mutations are a worry but not a surprise

WASHINGTON • Just as vaccines begin to offer hope for a path out of the coronavirus pandemic, officials in Britain this past weekend sounded an urgent alarm about what they called a highly contagious new variant of the coronavirus circulating in the country.

In South Africa, a similar version of the virus has emerged, sharing one of the mutations seen in the British variant, according to the scientists who detected it.

That virus has been found in up to 90 per cent of the samples whose genetic sequences have been analysed in South Africa since the middle of last month.

Scientists are worried about these variants but not surprised.

Researchers have recorded thousands of tiny modifications in the genetic material of the coronavirus as it has hopped across the world.

Some variants become more common in a population simply by luck, not because the changes somehow supercharge the virus.

But as it becomes more difficult for the pathogen to survive - due to vaccinations and growing immunity in human populations - researchers also expect the virus to gain useful mutations enabling it to spread more easily or to escape detection by the immune system.

"It's a real warning that we need to pay closer attention," said Dr Jesse Bloom, an evolutionary biologist at the Fred Hutchinson Cancer Research Centre in Seattle. "These mutations are going to spread, and definitely, the scientific community, we need to monitor these mutations, and we need to characterise which ones have effects."

The British variant has about 20 mutations, including several that affect how the virus locks onto human cells and infects them.

Dr Muge Cevik, an infectious disease expert at the University of St Andrews in Scotland and a scientific adviser to the British government, said these mutations may allow the variant to replicate and transmit more efficiently.

But the estimate of greater transmissibility - British officials said the variant was as much as 70 per cent more transmissible - is based on modelling and has not been confirmed in lab experiments, said Dr Cevik.

"We can't entirely rule out the fact that some of this transmissibility data might be related to human behaviour," she said.

In South Africa, too, scientists were quick to note that human behaviour was driving the epidemic, not necessarily the new mutations whose effect on transmissibility had yet to be quantified.

The British announcement also prompted concern that the virus might evolve to become resistant to the vaccines just now rolling out.

The worries are focused on a pair of alterations in the viral genetic code that may make it less vulnerable to certain antibodies.

But several experts urged caution, saying it would take years for the virus to evolve enough to render the current vaccines impotent.

Said Dr Bloom: "No one should worry that there is going to be a single catastrophic mutation that suddenly renders all immunity and antibodies useless.

"It is going to be a process that occurs over the time scale of multiple years and requires the accumulation of multiple viral mutations. It's not going to be like an on-off switch."

Like all viruses, the coronavirus is a shape-shifter. Some genetic changes are inconsequential, but some may give it an edge.

Scientists fear the latter possibility especially.

The vaccination of millions may force the virus to new adaptations, mutations that help it evade or resist the immune response.

Already, there are small changes in the virus that have arisen independently multiple times across the world, suggesting the mutations are helpful to the pathogen.

The mutation affecting antibody susceptibility is technically called the 69-70 deletion, meaning there are missing letters in the genetic code. The deletion changes the spike protein on the surface of the coronavirus, which it needs to infect human cells.

The Pfizer-BioNTech and Moderna vaccines induce an immune response only to the spike protein carried by the coronavirus on its surface. But each infected person produces a large, unique and complex repertoire of antibodies to this protein.

"The fact is that you have a thousand big guns pointed at the virus," said Dr Kartik Chandran, a virus expert at the Albert Einstein College of Medicine in New York.

"No matter how the virus twists and weaves, it's not that easy to find a genetic solution that can really combat all these different antibody specificities."

In short: It will be very hard for the coronavirus to escape the body's defences, despite the many variations it may adopt.

Escape from immunity requires that a virus accumulate a series of mutations, each allowing the pathogen to erode the effectiveness of the body's defences.

Some viruses, like influenza, amass those changes relatively quickly. But others, like the measles virus, collect hardly any of the alterations.

Dr Bloom noted that even the flu virus needs five to seven years to collect enough mutations to escape immune recognition entirely.

The scale of the infections in this pandemic may be quickly generating diversity in the new coronavirus. Still, a vast majority of people worldwide have yet to be infected, and that has made scientists hopeful.

University of Bern molecular public health researcher Emma Hodcroft said: "It would be a little surprising to me if we were seeing active selection for immune escape.... In a population that's still mostly naive, the virus just doesn't need to do that yet."

Immunising about 60 per cent of a population within about a year and keeping the number of cases down while that happens will help minimise the chances of the virus mutating significantly, she added.

Still, scientists will need to closely track the evolving virus to spot mutations that may give it an edge over vaccines.

NYTIMES