What Scientists Know About How the Coronavirus Variant Spreads

A more contagious form of the coronavirus has entered the United States.

In the UK, where it was first identified, the new variant became the predominant form of the coronavirus in just three months, accelerating that nation’s rise and filling its hospitals. It could do the same thing in the United States, exacerbating an unstoppable surge in deaths and overwhelming the already strained health system, experts warned.

One variant that is spreading more easily also means that people must follow religious precautions such as social distancing, mask-wearing, hand hygiene, and improved ventilation – undesirable news for many Americans who are already scrubbing against restrictions.

“The bottom line is that everything we do to reduce transmission is reducing transmission of all variants, including this one,” said Angela Rasmussen, a Georgetown University virologist. But “it may mean that the more targeted measures that aren’t like a full lockdown aren’t as effective.”

What does it mean for this variant to be transferable? What makes this variant more contagious than previous iterations of the virus? And why should we worry about a variant that spreads more easily but doesn’t seem to make anyone sick?

We asked experts to weigh the evolving research on this new version of the coronavirus.

Many variants of the coronavirus have emerged since the beginning of the pandemic. However, all evidence so far suggests that the new mutant, named B.1.1.7, is more transmissible than previous forms. It first appeared in the UK in September, but already accounts for more than 60 percent of new cases in London and neighboring areas.

The new variant appears to infect more people than previous versions of the coronavirus, even if the environments are the same. It is not clear what gives the variant this advantage, although there is evidence that it could infect cells more efficiently.

It’s also difficult to say exactly how much more transmissible the new variant can be, as scientists haven’t yet done the necessary laboratory experiments. Most of the conclusions were drawn from epidemiological observation and “there are so many possible biases in all the data available,” warned Muge Cevik, an infectious disease expert at the University of St Andrews in Scotland and a scientific advisor to the UK government.

Scientists initially estimated that the new variant was 70 percent more transferable, but a recent model study put that number at 56 percent. Once the researchers sift through all of the data, the variant may only be 10 to 20 percent more transmissible, said Trevor Bedford, an evolutionary biologist at the Fred Hutchinson Cancer Research Center in Seattle.

Still, said Dr. Bedford, it is likely to catch on quickly and become the predominant form in the United States by March. Scientists like Dr. Bedford closely follows all known variants to determine any further changes that could change their behavior.

The new mutant virus can spread more easily, but in every other way it seems little different from its predecessors.

At least so far, the variant does not seem to make people sick or lead to more deaths. Still, there is cause for concern: a more transmissible variant increases the death toll just because it spreads faster and infects more people.

“With that in mind, it’s just a numbers game,” said Dr. Rasmussen. The effect is amplified “in countries like the US and UK where the health system is really at its breaking point”.

The routes of transmission – through large and small droplets and tiny aerosolized particles floating in crowded interiors – have not changed. This means that masks, limiting time with others, and improving indoor ventilation will all help contain the spread of the variant, as it does with other variants of the virus.


Apr. 31, 2020 at 9:13 am ET

“By minimizing exposure to viruses, you reduce the risk of infection and overall transmission,” said Dr. Rasmussen.

Some preliminary evidence from the UK suggests that people infected with the new variant tend to have greater amounts of the virus in their nose and throat than people infected with previous versions.

“We’re talking in the 10-fold to 10,000-fold range,” said Michael Kidd, clinical virologist for Public Health England and clinical advisor to the UK government who has investigated the phenomenon.

There are other explanations for the finding: Dr. Kidd and his colleagues did not have access to information about when, for example, people were tested for their disease, which could affect what is known as their viral load.

However, the finding offers a possible explanation for why the new variant is spreading more easily. The more viruses infected people have in their noses and throats, the more they are expelled into the air and onto surfaces when they breathe, speak, sing, cough or sneeze.

As a result, situations where people are exposed to the virus are more likely to develop new infections. Some new data suggests that people infected with the new variant spread the virus to more of their contacts.

For previous versions of the virus, contact tracing suggested that about 10 percent of those who are in close contact with an infected person – for at least 15 minutes within six feet – inhaled enough virus to become infected.

“With the variant we could expect 15 percent of it,” said Dr. Bedford. “Right now, risky activities are getting riskier.”

The variant has 23 mutations compared to the version that broke out a year ago in Wuhan, China. But 17 of those mutations appeared suddenly after the virus deviated from its youngest ancestor.

Every infected person is a melting pot that gives the virus the opportunity to mutate as it reproduces. With more than 83 million people infected worldwide, the coronavirus is accumulating mutations faster than scientists expected at the start of the pandemic.

The vast majority of mutations offer no benefit to the virus and die out. However, mutations that improve the fitness or transmissibility of the virus have a greater chance of prevailing.

At least one of the 17 new mutations in the variant contributes to their greater contagion. The mechanism is not yet known. Some data suggest that the new variant may bind more tightly to a protein on the surface of human cells and infect them more easily.

It is possible for the variant to bloom in the nose and throat of an infected person, but not, for example, in the lungs. This may explain why patients are more likely to spread it but not develop more serious diseases than from previous versions of the virus. Some influenza viruses behave similarly, experts say.

“We must view this evidence as preliminary and accumulative,” said Dr. Cevik on the growing data on the new variant.

However, the studies to date indicate that the transmission of the variant must urgently be restricted. She added: “Overall, we need to be much more careful and investigate the gaps in our mitigation efforts.”

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