How does the coronavirus variant spread?
A more contagious form of the coronavirus has begun circulating in the US and elsewhere. In Britain, where it was first identified, the new variant became the predominant form in just three months,
accelerating that nation’s surge and filling its hospitals.
A variant that spreads more easily means that people will need to religiously adhere to precautions such as social distancing, mask-wearing, hand hygiene and improved ventilation — unwelcome news to many Americans already chafing against restrictions.
“Anything we do to reduce transmission will reduce transmission of any variants, including this one,” said Angela Rasmussen, a virus expert affiliated with Georgetown University, US. But “it may mean that the more targeted measures that are not like a full lockdown won’t be as effective.”
Many variants of the coronavirus have cropped up since the pandemic began. But all evidence so far suggests that the new mutant, called B.1.1.7, is more transmissible than previous forms. It first surfaced in September in Britain but already accounts for more than 60 per cent of new cases in London and neighbouring areas.
The new variant seems to infect more people than earlier versions, even when the environments are the same. It’s not clear what gives the variant this advantage, although there are indications that it may infect cells more efficiently.
It’s also difficult to say exactly how much more transmissible the new variant may be, because scientists have not yet done the kind of lab experiments that are required. Most of the conclusions have been drawn from epidemiological observations, and “there’s so many possible biases in all the available data,” cautioned Muge Cevik, an infectious disease expert at the University of St. Andrews in Scotland and a scientific adviser to the British government.
Scientists initially estimated that the new variant was 70 per cent more transmissible, but a recent modelling study pegged that number at 56 per cent. Once researchers sift through all the data, it’s possible that the variant will turn out to be just 10 to 20 per cent more transmissible, said Trevor Bedford, an evolutionary biologist at the Fred Hutchinson Cancer Research Center in Seattle, US.
The new mutant virus may spread more easily, but in every other way it seems little different than its predecessors. It does not seem to make people any sicker or lead to more deaths. Still, there is cause for concern: a variant that is more transmissible will increase the death toll simply because it will spread faster and infect more people.
The routes of transmission — by large and small droplets, and tiny aerosolised particles adrift in crowded indoor spaces — have not changed. That means masks, limiting time with others and improving ventilation in indoor spaces will still help contain the spread.
Infection with the new variant may increase the amount of virus in the body. Some preliminary evidence suggests that people infected with it tend to carry greater amounts of the virus in their noses and throats.
“We’re talking in the range between 10-fold greater and 10,000-fold greater,” said Michael Kidd, a clinical virologist at Public Health England who has studied the phenomenon.
There are other explanations for the finding — Kidd and his colleagues did not have access to information about when in their illness people were tested, which could affect their viral loads.
Still, the finding does offer one possible explanation for why the new variant spreads more easily. The more virus that infected people harbour in their noses and throats, the more they expel into the air and onto surfaces when they breathe, talk, sing, cough or sneeze.
As a result, situations that expose people to the virus carry a greater chance of seeding new infections. Some new data indicate that people infected with the new variant spread it to more of their contacts. With previous versions of the virus, contact tracing suggested that 10 per cent of people who have close contact with an infected person — within six feet for at least 15 minutes — inhaled enough virus to become infected.
“With the variant, we might expect 15 per cent of those,” Bedford said. “Therefore, currently risky activities become more risky.”
The variant has 23 mutations, compared with the version that erupted in Wuhan, China, a year ago. But 17 of those mutations appeared suddenly, after the virus diverged from its most recent ancestor. Each infected person is a crucible, offering opportunities for the virus to mutate as it multiplies. With more than 83 million people infected worldwide, the coronavirus is amassing mutations faster than expected.