Delta variant triggers dangerous new phase in the pandemic - Science Magazine

When the coronavirus variant now called Delta first appeared in December 2020, in the Indian state of Maharashtra, it did not seem all that remarkable.

But those protections seemed to barely slow Delta, which is more transmissible and may evade immunity, he says: “It went from a 10-foot wall around the city to a 2-foot wall you could just walk over.”.

“It is very likely that the Delta variant will circulate extensively during the summer, particularly among younger individuals that are not targeted for vaccination," she said.

The surge has set off a frenzy of research to understand why Delta appears to spread so much faster than the three other variants of concern, whether it is more dangerous in other ways, and how its unique pattern of mutations, which cause subtle changes in its proteins, can wreak havoc.

For the moment, Delta is a particular threat to the poorest countries with little or no access to vaccines, says Soumya Swaminathan, chief science adviser at the World Health Organization.

Compared with Alpha, which appeared in the United Kingdom in 2020, “You’re getting estimates of 50% or 100% more transmission,” says Adam Kucharski, a modeler at the London School of Hygiene & Tropical Medicine.

But Kucharski says reduced protection from vaccines may play a role as well.

The two effects—increased transmissibility and immune evasion—are hard to disentangle, but “I would argue the Delta variant has been driven by its transmissibility, not its ability to escape immunity,” says Jeremy Farrar, head of the Wellcome Trust.

“If Alpha really is approximately 50% more transmissible than the wild type strain, and Delta is 50% more transmissible again than Alpha, we’re talking about a virus that’s more than twice as transmissible as the initial strain,” adds Aris Katzourakis, an evolutionary virologist at the University of Oxford.

Indeed, if the faster spread “is entirely down to the fundamentals of the virus, that’s catastrophic news for the rest of the world,” Kucharski says.

One important mutation, called P681R, changes an amino acid at a spot directly beside the furin cleavage site, where a human enzyme cuts the protein, a key step enabling the virus to invade human cells.

In the Alpha variant, a mutation at that site made cleavage more efficient; a preprint published in late May showed Delta’s different change makes furin cleavage even easier.

Japanese researchers who made pseudo-viruses carrying the mutation have not found it to confer increased infectivity in the lab, however, and in India, other coronavirus variants that include the same mutation have been far less successful than Delta, says evolutionary virologist Andrew Rambaut of the University of Edinburgh.

Delta’s unique mutations delete the amino acids at positions 156 and 157 in the supersite and changes the 158th amino acid from arginine to glycine; the latter eliminates a direct contact point for antibody binding, says David Ostrov, a structural biologist at the University of Florida.

And scientists should start to examine the role of changes in other Delta variant proteins, says Nevan Krogan, a molecular biologist at the University of California, San Francisco.

We are so in the dark.” Delta has several mutations in the nucleocapsid protein, for example, which has many jobs, “like a Swiss Army Knife protein,” says virologist David Bauer of the Francis Crick Institute.

“Worries about Delta should galvanize us to really ramp up vaccination efforts and surge vaccines to places where Delta is ticking up,” says virologist Angela Rasmussen of the University of Saskatchewan.

Ammon today called on European countries to accelerate plans to fully vaccinate vulnerable populations; in the meantime, she said, restrictions should be kept in place to keep the new variant from spreading and causing another surge in cases, hospitalizations, and deaths.

Delta’s success has shown scientists aren’t able to identify dangerous new variants in time to stop them spreading, says Emma Hodcroft, a virologist at the University of Basel, despite an unprecedented global effort to track its evolution in real time.