Nature reveals: Children's outstanding performance in response to the new crown, Delta strain, makes "supernatural power" disappear

Article source: Medical Rubik's Cube Pro

Author: Haimer

The recent epidemic in Fujian Province has once again moved people's hearts

Coincidentally, data released by the American Academy of Pediatrics (AAP) on September 7 showed that among the newly diagnosed cases of new coronary pneumonia in the United States in the week of August 26, child cases accounted for 26.

At the beginning of the COVID-19 pandemic, children had obvious advantages over adults in dealing with SARS-CoV-2

How do children differ from adults in responding to SARS-CoV-2? Why is the proportion of children diagnosed recently on the rise? On September 7, the article Kids and COVID: why young immune systems are still on top published on Nature tried to answer these questions

Quiet children's ward

When the COVID-19 epidemic first began, it was found that children and adolescents appeared to be less common among confirmed cases

Data from the Centers for Disease Control and Prevention (CDC) also show that between March 2020 and late August 2021, a total of 3,649 children and adolescents under the age of 18 were hospitalized due to the new crown in the United States, accounting for less than 2% of the total number of hospitalizations.

This is contrary to people's past experience.

The outstanding performance of children and young people in response to the new crown surprises the outside world

Delta brings new uncertainty

With the prevalence of the more transmissible Delta variant and the increase in adult vaccination rates, the proportion of children in new infections is gradually increasing

Source: Nature

This trend is even more pronounced in the epidemiological studies in Israel

Source: Nature

There is still no clear evidence that children are more susceptible to the Delta strain.

Surprisingly non-specific immunity

The special advantages of children in the fight against SARS-CoV-2 have aroused widespread attention of scientists, and many conjectures have been put forward

Some researchers believe that the small number of angiotensin-converting enzyme 2 (ACE2) receptors in children prevents the virus from invading cells.

There is also a hypothesis that children are more likely to be exposed to some other coronaviruses, and the antibodies produced can cross-protect SARS-CoV-2

After collecting some evidence, the Herold team basically rejected the above conjectures and began to concentrate on studying the characteristics of children when fighting against SARS-CoV-2

In an analysis of the blood of infected persons, Herold found several differences between children and adults

In contrast, the children’s group has higher levels of signal proteins interferon-γ and interleukin-17 (IL-17), which act as a reminder of the immune system when pathogens invade the body
.
Herold guessed that children's specific immune response is weak, because their non-specific immune response is very high, and the overactive specific immune response of adults can cause some complications of the new crown
.

The patient's nasal and throat swab samples collected by the Herold team from the emergency department also verified the above conjecture
.
Children have higher levels of signaling proteins, such as interferons and interleukins, and higher levels of genes encoding these proteins
.

Lael Yonker, a pediatric pulmonologist at the Massachusetts General Hospital (MGH), also discovered that innate lymphocytes (ILC) in children may also play an important role
.
ILC is one of the first immune cells to detect tissue damage, and can secrete signal proteins that regulate non-specific immunity and specific immunity
.

In addition, the researchers also found that children have higher expression levels of the gene encoding MDA5 than adults
.
MDA5 is a receptor that recognizes SARS-CoV-2.
After a pathogen is found to invade the human body, it can immediately trigger the production of interferon and other signaling proteins
.
Roland Eils, a genomics scientist at the Berlin Institute of Health Research, said that it takes two days for adults to increase the immune system’s defenses against viruses to the level of children
.
The time lag determines the different reactions of children and adults to the virus
.

Not only in the new coronary pneumonia, but also in other respiratory infections such as influenza, non-specific immunity has played a leading role
.

"Experience" becomes an obstacle

Some researchers have suggested that another reason why children are more advantageous in the fight against SARS-CoV-2 may be the "originalantigenic sin", also known as the "Hoskin phenomenon
.
"

Antigenic crime means that when the body is exposed to a pathogen similar to the first infection, it tends to use the past immune memory instead of regenerating an immune response
.
This results in the body's inability to produce the most effective immune response against specific antigens
.
Children's immune memory is far less than that of adults, which promotes the immune system to produce a new and more effective immune response
.

This conjecture was confirmed by a study of antibodies in hundreds of children and adults in Australia
.
Researchers have found that adults’ cross-reactive antibodies are more directed against SARS-CoV-2 and other coronavirus fragments similar to parts, while children’s immune systems are more "hard-working" and tend to produce a wider range of antigen fragments of the virus.
Antibody
.

Promote minor vaccination

With the increase in the proportion of minors who are infected, China will gradually promote the vaccination of minors
.

On September 7, at a press conference held by the Joint Prevention and Control Mechanism of the State Council, Wang Huaqing, chief expert of the China Centers for Disease Control and Prevention's immunization program, answered reporters' questions about children's infection with the new crown
.

Wang Huaqing believes that there are three main reasons for the increasing infection rate in children: one is the prevalence of the more infectious Delta strain; the other is that immunization is started from the elderly and key populations, and child vaccination has not yet been officially included in the schedule.
As a result, children’s immunity is low; the third is the adjustment of prevention and control measures, and the overall prevention and control measures have been relaxed, which has led to an increase in the infection rate of children
.

"In response to the current increase in children's infections, many countries have adopted vaccination measures, including our country, which has also included the vaccination of children and adolescents on the agenda.
At present, the vaccination is being carried out in stages, focused and scientifically
.
"

Reference materials:

[1] Smriti Mallapaty, Kids and COVID: why young immune systems arestill on top.
Nature.
(2021)

[2] Smriti Mallapaty, Will COVID become a disease of the young? Nature.
(2021)

[3] Pierce, CA et al.
JCI Insight 6, e148694 (2021).

[4] The State Council's Joint Prevention and Control Mechanism will hold a press conference at 15:00 on September 7, 2021 in the Xizhimen Office of the National Health Commission to introduce the situation of further epidemic prevention and control and vaccination, and answer media questions (source : China Government Network)