Why does Omicron only cause "mild disease" while children infection soared?

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Why does Omicron only cause “mild disease” while children infection soared?

Mankind’s fight against the epidemic has entered a new year, and the end of this tug-of-war still seems to be far away.

Recently, Omicron has increased the number of single-day cases in the United States by the order of one million, which is really worrying.

The well-known American infectious disease expert Fauci said that now we should not pay attention to the number of cases, but to the number of hospital admissions. The main reason is that Omicron cases are mild. .

Why does Omicron only cause “mild disease” at present? Recently, a study on the bioRxiv preprint stated that this was mainly caused by the accumulation of viruses in the upper respiratory tract…

At the same time, it also gave an explanation for the high infection rate in children: because children have short respiratory tracts, and they mainly use their noses to breathe. This pushed up the infection rate among children.

However, we do not just believe that Omicron is low in lethality. The researchers said that we basically do not know the long-term negative effects of the COVID-19 infection.

They also believe that we should not overemphasize the mortality and hospitalization rate, but should pay more attention to the burden of diseases brought by the COVID-19 in the future , such as the sequelae of the COVID-19. Previous studies have found that the COVID-19 has long-term damage to the taste of some people.

At the end of 2021, Omicron broke into human life unexpectedly and spread to the world. At first, we panicked about it, and then it mainly caused mild illness, and let us put down our vigilance.

At the beginning of the new year, the Omicron-led epidemic broke out in Europe and the United States: the number of new patients was “blowout” in many places , and the epidemic in the United States rebounded sharply.

Both the new single-day and cumulative Omicron cases broke historical records, and Europe has reported it.

Accumulated more than 100 million confirmed cases of COVID-19, accounting for more than one-third of all infections worldwide.

This may be related to the particularity of the virus strain Omicron: the mild symptoms caused by it are more pronounced than previous strains, making public opinion that soothes public opinion and the US government’s “lying flat” behavior “there are laws to follow.”

However, the scientist camp is still on the front line researching the current leader of the new coronavirus camp Omicron, exploring its infection mechanism, pathogenic mechanism and its position in the new coronavirus family, which are very important for prevention and control work and vaccine research and development.

The following is the latest research on the causes of Omicron’s “mild” disease. However, the research results are still under consideration in the preprint.

The research team measured the virus concentration in the lungs of the sample mice, and used the body weight of the mice to quantify the damage to the body organs of different mutant strains.

The concentration of the virus in the lungs of experimental samples infected with Omicron was at least ten times lower than that of rodents infected with other new coronavirus mutants. It can be seen that compared with the previous new coronavirus mutants, Omicron has a lower viral load in lung tissue.

At the same time, the research team also found that the body weight of the animals in the Omicron sample group remained basically unchanged, while the body weight of the animals in the other groups dropped rapidly .

Why does Omicron only cause "mild disease" while children infection soared? a, b, the average weight change of hamsters infected with various mutants

c, d, the average weight change of hamsters infected with Omicron stock 1 and stock 2, showing the average weight change

Under normal circumstances, the new coronavirus can cause severe lung infections and trigger an inflammatory immune response, destroying cellular tissues, leading to scar formation and hypoxia in the body. If there are fewer lung cells that are infected, it may mean that the disease is milder. So the research team also used a miniature lung model called an organoid , and the results showed that Omicron can infect lung cells much less than previous mutants.

Why does Omicron only cause "mild disease" while children infection soared? a and b respectively indicate the level of E subgenomic RNA (sgRNA) in the lung and turbinate after the hamster is infected with various mutants,
N-genomic RNA (gRNA) levels. The red bar depicts the median.

Previous studies have shown that the COVID-19 mutant uses a protein called TMPRSS2 to fuse the cell membrane to cause infection.

Unlike the Omicron strain, it prefers to enter the cell through direct fusion with the cell membrane and does not bind well to TMPRSS2. So TMPRSS2 was introduced as a variable of observed difference.

Why does Omicron only cause "mild disease" while children infection soared? New Coronavirus Infected Cells | Image Credit: Janet Iwasa, University of Utah

The results show that this protein is protruding on the surface of many cells in the lungs and other organs (easy to bind to the new coronavirus) , but it is missing on the surface of most nose and throat cells, indicating that Omicron is more destructive to the lungs The respiratory tract is light.

Why does Omicron only cause "mild disease" while children infection soared?
Histopathological examination image of hamster on the 4th day after infection. a, There is interstitial inflammation associated with bronchioles, multifocal areas with patchy consolidation. b, Medium power representative image of bronchial epithelium. Epithelial degeneration is characterized by cilia loss, loss of nuclear polarity and airway entry, accompanied by consolidation of mandibular lung parenchyma.

Through the above series of studies, researchers can provide a relatively convincing explanation for the difference in symptoms of the cases: Omicron is not as easy to infect cells deep in the lungs as cells in the upper respiratory tract.

Researchers guess that Omicron is more infectious than measles. If it is because most of the virus is entrenched in the upper respiratory tract, and high concentrations of virus particles are discharged from the nose and mouth through breathing, it seems that everything can be explained.

During the Omicron epidemic, the child infection rate surged? The explanation given by the researchers is that, theoretically, because the nasal cavity of young children is relatively small, and babies only breathe through the nose, children’s upper respiratory tract diseases are often more serious than adults.

Therefore, we need to pay attention to the health of children’s respiratory tract, but there is currently no data to show that the number of such hospitalized children has increased (the presence of symptoms such as laryngotracheobronchitis indicates severe upper respiratory tract infection) .

Some professionals commented that the concerns caused by the numerous mutations in the Omicron genome in late November have not been fully confirmed, but the initial alert provided a warning: How the virus infects organisms only from its genetic sequence is still a mystery.

references
https://www.nature.com/articles/d41586-022-00007-8
https://www.biorxiv.org/content/10.1101/2022.01.02.474743v1.full
https://www.nature.com/articles/d41586-021-03794-8