The fifth wave of the new coronavirus, which was the largest spread of infection ever.
It seems that the peak has finally passed, but as the highly infectious "Delta strain" became mainstream, some people began to think that "the new corona will be infected by air".
Isn't the new corona "flying infection" and "contact infection"?
Is it mutated to be airborne?
I have summarized what I know now.
"Micro-flying" infection noticed by Japanese experts
In February 2020, when the infection of the new corona began in Japan, Japanese experts who took measures noticed the characteristics of the infection.
At that time, WHO = World Health Organization and others said that the new corona was "flying infection" through the virus contained in the flying squirrel that was issued when coughing, and that it spreads by touching the nose and mouth with the virus-attached hand. I've called it "contact infection" ...
If you look closely at cases infected indoors, such as cases infected at a resting place that was warm at the Sapporo Snow Festival, there are infection routes that go beyond that.
It was found that a tiny flying object containing a virus floated for a while in an enclosed space and was infected by inhaling it.
I noticed that there was an infection caused by "micro-flying" floating in space, unlike "flying" that falls quickly.
Based on this discovery, in addition to avoiding hand washing, disinfection, and conversation without a mask, measures to avoid the three densities of "sealing, dense, and close" were born, and they have been introduced in WHO and others. ..
Now that the Delta strain has become mainstream, is it even more susceptible to infection and something like "airborne transmission" is happening?
What kind of infection is "airborne infection"?
Before that, what kind of infection is airborne infection?
The saliva and other flying particles from the infected person dry out, and the pathogens in them float in the air and spread while maintaining their infectivity.
"Airborne infection" is caused by inhaling this.
It is said that countermeasures are the most difficult because "flying nuclei" with a diameter of 5 micrometers and less than 5/1000 mm float for several hours and are inhaled and infected by people in the same space.
It is said that if you cough in a remote place in the same room, for example, in the front row of the classroom, you can get infected even in the back.
However, according to the CDC = Centers for Disease Control and Prevention in the United States, airborne infections are limited to Mycobacterium tuberculosis, measles, chickenpox, and herpes zoster viruses.
If measles is not taken, it will infect 1 to 12 to 18 people.
Although the new corona is smaller than the "flying pine", it is not as small as the "flying nucleus", and it has been said that there is infection with the "micro flying pine" that floats in a certain time and space.
Possibility of infectivity of Delta strain "similar to chickenpox"
So what about Delta stocks?
The website where the CDC describes the infectivity and spread of Delta strains states that it is more than twice as infectious as before and can be more severe without vaccination. There is no description about "airborne infection".
In addition, although the government's subcommittee made a proposal in the middle of last month that "the highly infectious delta strain is more likely to cause the spread of infection", "the main infection mode is the same as before, and it flies. Or it is considered to be a micro-fly, and it is necessary to thoroughly implement the measures so far. "
On the other hand, according to the CDC's internal data, one patient could infect an average of 1.5 to 3.5 people with the conventional virus, whereas the Delta strain can infect an average of 5 to 9.5 people. It is estimated that, if any, it may have "the same level of infectivity as chickenpox" in the highest case.
Experts point out the possibility of “effects of high virus volume”
Professor Kazuhiro Tateda of Toho University, a member of the government's subcommittee on measures against the new coronavirus, said that although it is certain that the Delta strain is highly infectious, it has not been proven to be infected by air at present. Says.
"To prove that you are" airborne ", the water in the flying pine from the infected person evaporates, and the virus remains in the" flying nucleus "and floats in the air to cause infection. Such a condition needs to be observed. The new corona has not been proven to that extent yet. ”
Professor Tateda said that the strong infectivity of the Delta strain is due to the large amount of virus excreted by the patient. I will point out the possibility of being infected.
"Although it is being proven clinically, it is possible that the viral load is very high, so we must carefully analyze whether it looks like an airborne infection."
Viral load estimated to be more than 4 times that of conventional private inspection companies
Although not proven to be airborne, the Delta strain is so infectious.
Further interviews revealed that there was data to support this.
Private sector testing companies have found that the Delta strain is estimated to detect at least four times as much virus in patients as the traditional new coronavirus.
The data was compiled by BML, a major testing company that conducts up to 20,000 PCR tests a day.
In the PCR test, the genes contained in the sample are amplified to check for the presence of virus.
The number of times of amplification is called "Ct value", and generally, when this value is within 40, it is considered as "positive".
If the "Ct value" is low but detected, it indicates that the amount of virus is high.
When we examined the percentage of "Ct value" that was less than 20 times, which was half of the 40 times that were positive,
▽ 38.0% of the total in January ▽ Even in April when the
first confirmed alpha strain in the UK spread It was 41.4%.
That was as
65.9% in July, when Delta stocks became mainstream, and
63.7% last month.
Based on the Ct value, which was the most frequent in each period, the amount of virus contained in the sample is considered to be at least 4 to 64 times higher in the Delta strain than in the conventional and alpha strains. about it.
Toshikazu Yamaguchi, executive officer of "BML," said, "Since July, we have frequently seen specimens with a clearly low Ct value and a large amount of virus. This is a difference compared to conventional viruses. I didn't imagine there was a decisive difference in viral load. "
Take measures on the premise that the amount of virus is large
Regarding this data, Professor Tateda says that it is the first time that domestic data has shown that the amount of virus detected in patients is high in Delta strains.
And, assuming that the amount of virus is large,
▽ Wear a non-woven mask
▽ Keep a distance between people
when eating and drinking
Wear a mask when talking when eating and drinking
▽ Thorough ventilation It is important to take measures such as things.
Ventilation is especially important, and it is important to do it once or twice an hour for 5 to 10 minutes at a time.
On top of that, "It has been reported that the virus tends to maintain its infectivity in the air when the temperature is low. It must be considered that the risk of infection increases as the temperature drops in the fall and winter. It is important to take thorough measures. Even if you take a vaccine, you may be spreading the infection without knowing it, so please be alert and take measures. "
"Airborne infection" Thorough countermeasures even if there is no clear evidence
At present, we have not found clear evidence of airborne transmission of Delta strains.
However, it is a fact that it is highly infectious, and data supporting it has been reported.
Even in highly vaccinated countries, the Delta strain has re-spread the infection, so there is no doubt that thorough ventilation is required in addition to the measures taken so far.Keywords: