New research in laboratory animals and human tissues provides the first indication of why the Omigron variant causes milder disease than previous versions of the corona virus.

In studies on mice and hamsters, Omigron developed less damaging infections, mostly in the upper respiratory tract: nose, throat and trachea. This variant was less harmful to the lungs, where previous variants often caused scarring and severe respiratory distress.

Roland Eels, a computational biologist at the Berlin Institute of Health, says: “It is fair to say that the idea of ​​a disease primarily appearing in the upper respiratory tract emerges. Studied How corona viruses affect the airways.

In November, the first report was released on Omigron variant Originally from South Africa, only scientists have been able to predict how it will behave differently from previous forms of the virus. They only know that it contains a unique and dangerous combination of more than 50 genetic mutations.

Previous research has shown that some of these mutations help corona viruses to hold cells tightly together. Others allowed viral antibodies to be avoided, which acted as a starting line for protection against infection. But how the new variant could behave inside the body remained a mystery.

Ravindra Gupta, a virologist at the University of Cambridge, said: “You can not predict the behavior of a virus by mutations.

Over the past month, a dozen research teams, including Dr. Gupta, have observed a new pathogen in the laboratory, infecting cells in Petri foods with Omigron and spraying the virus on the noses of animals.

When they did, Omigron spread throughout the planet, immediately affecting even those who had been vaccinated or survived an infection.

But as the number of cases increased, so did the number of hospital admissions. Early studies of patients suggested that Omicron was less likely to cause serious illness than other types, especially in vaccinated people. However, those findings came with a lot of warnings.

For one, the vast majority of early Omigran infections were in young people, who were less likely to become seriously ill in all versions of the virus. Many of those early cases occurred in people who had some immunity from previous infections or vaccinations. For example, it is unclear whether Omigran will prove less severe in an older person who has not been vaccinated.

Experiments on animals will help clear up these ambiguities because scientists could test Omigran in the same animals that live in the same condition. More than half a dozen tests have been released in recent days, all of which point to the same result: Omigron is lighter than other previous versions of Delta and Virus.

On Wednesday, a large consortium of Japanese and American scientists was released Report In hamsters and mice infected with Omigran or one of several earlier species. The study found that people with Omicron disease had lower lung damage, lower weight loss and lower risk of death.

Although animals infected with Omicron disease generally experience mild symptoms, scientists have been particularly struck by the results of Syrian hamsters, a species that has been severely infected by all previous versions of the virus.

“It was amazing because all the other species were so strongly affected by these hamsters,” said Dr. Michael Diamond, a virologist at the University of Washington and co-author of the study.

Many Others Studies on Mice And Hamsters Have come to the same conclusion. (Like most urgent Omigron research, these studies have been published online, but have not yet been published in scientific journals.)

The reason Omigran is mild may be anatomical. Dr. Diamond and his colleagues found that the level of omigran in the nose of hamsters was similar to that in animals previously infected with the corona virus. But omigron levels in the lungs were one-tenth or less of the level of other variants.

A A similar finding It came from researchers at the University of Hong Kong who examined pieces of tissue taken from the human respiratory tract during surgery. In 12 lung samples, the researchers found that Omigron grew more slowly than Delta and other types.

The researchers also found that tissue from the trachea, a tube in the upper part of the chest that supplies air from the trachea to the lungs. Within those bronchial cells, Omigron grew faster than the delta or original corona virus within the first two days of infection.

These findings should be followed up with further studies, such as experiments with monkeys or examining the airways of victims of Omigran. If the results are scrutinized, they could explain that those affected by Omigran are less likely to be hospitalized than those in Delta.

Corona virus infection starts in the nose or maybe Mouth And spread down the throat. Mild infections are no more than that. But when the corona virus reaches the lungs, it can cause severe damage.

The immune cells in the lungs overheat and kill not only the infected cells but also the unaffected cells. They create runway inflammation and scar the soft walls of the lungs. What’s more, the viruses leave the damaged lungs in the bloodstream, triggering blood clots and destroying other organs.

Dr. Gupta suspects that his team’s new data could provide a molecular explanation for why Omigran does not function so well in the lungs.

Many cells in the lungs carry a protein called TMPRSS2 to their surface, which allows viruses to inadvertently enter the cell. But Dr. Gupta’s team found that this protein did not work well in Omigran. As a result, Omicron does a worse job of affecting cells in this way than Delta. A team at the University of Glasgow Independently came to the same conclusion.

Alternatively, corona viruses may infect cells that do not produce TMPRSS2. At higher altitudes in the airway, cells do not carry protein, which explains the evidence that omigran is more frequently found in the lungs.

Dr. Gupta speculated that Omigran had evolved into an over-the-air specialist, thriving in the throat and nose. If that is true, there is a good chance that the virus will be expelled in small droplets in the surrounding air and meet new hosts.

“It’s about what’s going on in the air above the spread, isn’t it?” he said. “It’s not really going down in the lungs, there’s serious disease things going on. So you can understand why the virus has developed this way.

Although these studies clearly help to explain why Omigron causes mild disease, they have not yet responded to why this variation spreads from one person to another. United States logged in More than 580,000 cases On Thursday alone, most are considered omigran.

“These studies address the question of what can happen in the lungs, but do not really address the question of contagion,” he said. Sarah Cherry is a virologist at the Pearlman School of Medicine at the University of Pennsylvania.

Dr. Diamond said he would like to wait for further research to be carried out, especially in humans, instead of animals, before recognizing that DMPRS2 is the key to understanding Omigran. “I think it’s still too early,” he said.

Scientists know that part of Omigran’s infectivity comes from its ability to block antibodies, which allow it to enter the cells of vaccinated people more easily than other types. But they suspect that Omigran has some other biological benefits as well.

Last week, researchers Reported This variant has a mutation that weakens the so-called innate immunity, which is a molecular alarm that activates our immune system rapidly as the first sign of invasion. Nose. But many more tests will be needed to see if this is really one of the secrets to Omicron’s success.

“It can be very simple, it has more virus in people’s saliva and nasal passages,” Dr. Cherry said. But there may be other explanations for its effective spread: It can be very stable in the air or better affect new hosts. “I think this is an important question,” he said.