New stage of pandemic: dangerous strain "Delta"

2024 Author: Seth Attwood | [email protected]. Last modified: 2023-12-16 15:55

The new Indian strain covid-19, already named by scientists "Delta", has spawned the third wave of the pandemic in many countries. In New Delhi itself, the situation is simply catastrophic - 30,000 cases per day. The institutes began to study the "Delta" and immediately sounded the alarm.

The new strain turned out to be not only more infectious, but also less vulnerable to antibodies. This means that he can successfully resist the "counterattacks" that our immune system will lead against him.

When the variant of the coronavirus, now dubbed "Delta", first appeared in the Indian state of Maharashtra in December 2020, it did not appear to be anything special. But when it hit New Delhi a few months later, the consequences were most devastating, with nearly 30,000 cases every day at the end of April. “Suddenly, he began to dominate and completely crushed the Alpha strain, which until then was the most widespread in the city,” says Anurag Agrawal, head of the Institute of Genome and Integrative Biology in New Delhi.

New Delhi seemed unlikely to face another major outbreak, Agrawal said, as many of its residents were either sick or vaccinated. But it turned out that these means of defense against Delta are powerless. It is more infectious and escapes the immune system, he says: "The three-meter wall around the city seemed to have turned into a half-meter one, over which it is not difficult to step over."

From New Delhi, the strain has spread rapidly and now appears to be sweeping the globe with a new, devastating wave. In the UK, Delta already accounts for more than 90% of new cases: this has caused the number of cases of coronavirus to jump again after a sharp decline, and last week the government even had to postpone the final phase of its border opening plan. The outbreak of the Delta in Lisbon forced the Portuguese government to impose a three-day travel ban between the capital and the rest of the country.

By the end of August, this option will account for up to 90% of all cases of coronavirus in the European Union, the head of the European Center for Disease Prevention and Control Andrea Ammon warned today. “It is very likely that the Delta strain will spread widely during the summer, especially among young people who are not part of the vaccination program," she said. “This could put more vulnerable citizens at risk of becoming seriously ill or even dead. if they are not fully vaccinated."

The Delta races have been recorded in Russia, Indonesia and many other countries. In the US, where the prevalence of the strain is estimated to be at least 14%, the CDC said on June 15 that it was "of greatest concern."

The upsurge has sparked a string of studies to understand why Delta is spreading much faster than the other three worrying variants, if it is otherwise more dangerous, and how its unique set of mutations that cause changes in the protein environment can cause serious damage. The arrival of Delta highlighted that the SARS-CoV-2 virus can adapt and evolve over the coming months and years.

At the moment, Delta poses a particular threat to the poorest countries, whose access to vaccines is limited or completely absent, says Sumya Shwaminathan, chief scientific adviser to the World Health Organization. “What worries me the most is what will happen when Delta gets to Africa,” she says.

A study by Public Health England has highlighted the proliferation potential of Delta. Compared to Alpha, which launched in the UK in 2020, “we have 50% or 100% more transmissions,” says Adam Kucharski, model developer at the London School of Hygiene and Tropical Medicine.

But Kuharsky also says that the decrease in protection from vaccines could have affected. Pfizer-BioNTech and AstraZeneca vaccines provide slightly less protection against symptomatic infections with the new variant than for the Alpha strain based on data from England and Scotland. People with just one shot are especially vulnerable - as are many in the UK. (Two doses of any vaccine will still provide the same high level of protection against hospitalization, even against Delta.) How well other vaccines used around the world are protecting is unclear, and there is little evidence of protection in those who have recovered from past waves of coronavirus.

Both of these effects - increased transmission and immunity evasion - are difficult to separate from each other, but the head of the Wellcome Trust, Jeremy Farrar, believes that transmission is behind the Delta jump, not immunity bypass. "If Alpha is about 50% more transmissible than the natural strain, and Delta is another 50%, then we are talking about a virus that is twice as transmissible than the original strain," explains an evolutionary virologist from Oxford Aris Katzourakis University.

This will mean that countries and populations with low vaccination rates could face large new outbreaks. “If the faster spread is entirely due to the virus's underpinnings, then this is disastrous news for the rest of the world,” says Kuharski.

On top of that, Delta is more likely to send unvaccinated citizens to hospital than Alpha. Early data from the UK suggests that the risk of hospitalization could be twice as high. Taken together, these characteristics could cause huge problems in Africa, Schwaminathan said. “There won't be oxygen, there won't be enough hospital beds. And we already know that hospital outcomes in Africa are worse than in other countries, she says. "So it can really lead to higher mortality rates even among young people."

Mutations interfere with antibodies

Scientists have just begun to figure out why Delta is so dangerous. They focused on a set of nine mutations in a gene that encodes a spike protein that probes the surface and allows the virus to enter human cells. One important mutation, dubbed P681R, changes an amino acid just next to the furin cleavage site where a human enzyme cleaves the protein - a key step that allows the virus to enter human cells.

In the Alpha strain, this mutation made cleavage more efficient. According to one preliminary publication in late May, Delta mutations make it even easier for furin to break down. The researchers speculate that this could also increase the transmissibility of the virus.

However, Japanese researchers who created pseudoviruses carrying the same mutation did not confirm the increased infectivity in laboratory conditions, and in India, other variants of the coronavirus with the same mutation turned out to be much less infectious than Delta, says evolutionary virologist at the University of Edinburgh, Andrew Rambaut). "So there must be interaction with something else in the genome."

Other Delta mutations can help undermine immunity. Some of them alter the N-terminal domain of the spine (NTD) that protrudes from the surface of the protein. In a recent article in the journal Cell, it was revealed that one of the NTD spots, dubbed "super-site", invariably targets "super-potent" neutralizing antibodies from recovered patients. The unique Delta mutations remove amino acids at positions 156 and 157 of the “superfrequency” and change amino acid 158 from arginine to glycine - the latter eliminating the direct contact point for antibody binding, explains University of Florida structural biologist David Ostrov.

"We believe the 157/158 mutation is one of the distinctive Delta mutations that gave the strain this immunity evasion phenotype," agrees Trevor Bedford, a computer biologist at the Fred Hutchinson Cancer Research Center.

Another mutation in the NTD super-region can also fight off antibodies. And scientists must begin to study the role of changes in other Delta proteins, says Nevan Krogan, a molecular biologist at the University of California, San Francisco. “There is a lot we don’t know about these options at every level. We seem to be wandering in the dark. " For example, "Delta" has several mutations in the nucleocapsid protein, which performs many functions "like a Swiss army knife," explains virologist David Bauer of the Francis Crick Institute. However, it will take months to experiment to clarify.

Accelerated vaccination

Meanwhile, scientists agree: urgent action is needed to stop the spread of the new variant. “Delta concerns should motivate us to really accelerate vaccination and increase vaccine availability in the field where Delta is gaining traction,” said virologist Angela Rasmussen of the University of Saskatchewan. US President Joe Biden has called on Americans to get a full vaccination to protect themselves from Delta. Ammon today called on European countries to accelerate plans to fully vaccinate vulnerable populations.

In addition, she said, restrictions must be maintained so that the new option does not spread and entail a new surge in morbidity, hospitalizations and deaths. Countries with limited access to vaccines need to revert to measures such as physical distancing and masks, Rasmussen said. And in Europe, Ammon urged countries to do both: maintain restrictions while working to fully vaccinate vulnerable populations.

The goal is not only to save lives, but to prevent the further development of the virus. The spread of Delta has shown that scientists are unable to recognize dangerous new variants in time to stop their spread, says Emma Hodcroft, a virologist at the University of Basel, despite unprecedented global efforts to track their evolution in real time. It would be dangerous to assume SARS-CoV-2 would stop there, Katsurakis said. “Everything in evolution that has happened at least twice is already a pattern,” he says. "I wouldn't be surprised if we see similar changes in the next year or two."