＜prologue＞
I started a blog called “The Baby Boomer Generation’s Miscellaneous Blog”（Dankai-sedai no garakutatyou:団塊世代の我楽多（がらくた）帳） in July 2018, about a year before I fully retired. More than six years have passed since then, and the number of articles has increased considerably.
So, in order to make them accessible to people who don’t understand Japanese, I decided to translate my past articles into English and publish them.
It may sound a bit exaggerated, but I would like to make this my life’s work.
It should be noted that haiku and waka （Japanese short fixed form poems） are quite difficult to translate into English, so some parts are written in Japanese.
If you are interested in haiku or waka and would like to know more, please read introductory or specialized books on haiku or waka written in English.
I also write many articles about the Japanese language. I would be happy if these inspire more people to want to learn Japanese.
my blog’s URL:団塊世代の我楽多（がらくた）帳 | 団塊世代が雑学や面白い話を発信しています
my X’s URL:団塊世代の我楽多帳（@historia49）さん / X
<Added October 11, 2020> The US Centers for Disease Control and Prevention (CDC) has admitted that the virus is “airborne” after several twists and turns.
In response to the question “Is COVID-19 pneumonia airborne?”, the US Centers for Disease Control and Prevention (CDC) initially denied the possibility, but after several twists and turns, it has now reportedly admitted that “it can sometimes be airborne.”
In early July, the World Health Organization (WHO) stated that “the possibility of airborne transmission in crowded, poorly ventilated spaces cannot be ruled out,” but it took three months for the CDC, which leads the world in disease prevention efforts, to acknowledge this.
As the global spread of the COVID-19 coronavirus pneumonia (pandemic) continues, a concerning story has recently emerged.
Japan is currently trying to prevent an infection explosion (overshoot) by identifying infection routes to contain cluster infections, avoiding crowded places, and encouraging people to stay at home. However, in the US, New York State has conducted antibody tests and reportedly found more than 10 times the number of COVID-19 infected people as confirmed by PCR tests.
An analysis by the University of Southern California, based on antibody tests using samples conducted in California, suggests that 28 to 55 times as many people may already be infected as compared to the number of confirmed cases at medical institutions.
However, while antibody tests have the advantages of being simple, providing results quickly, and being inexpensive, they are also said to have accuracy issues.
It appears that COVID-19 has now moved beyond the stages of contact and droplet transmission and is now spreading through the air.
Also, is herd immunity inevitable until a vaccine or treatment is developed?
We’ve also heard that people can test positive again even after recovering from COVID-19, and that the virus can mutate within the body. It seems to be a very nasty and tough virus.
1. Is the spread of the virus now airborne in Japan?
It has traditionally been said that COVID-19 is not airborne. Dr. Masahiro Yamaguchi, an infectious disease specialist in Kitakyushu City, points out that “if it were airborne like measles or tuberculosis, the scale of outbreaks would be much larger.”
However, on April 25th, on Asahi Broadcasting Corporation’s news commentary program “Tell Me! News Live: Justice’s Friend” (every Saturday from 9:30 AM to 11:00 AM), former Ministry of Health, Labor and Welfare medical engineer Moriyo Kimura expressed the view that “the coronavirus is now airborne.”
It is true that we have heard that “some people are infected but asymptomatic,” so I think that airborne transmission of the coronavirus cannot be ruled out.
Isn’t it more natural to understand that the recent increase in the proportion of people with “unknown infection routes” among Tokyo’s infected people is due to airborne transmission?
<Added July 8, 2020> The WHO finally announces that “the possibility of airborne transmission cannot be ruled out.”
Dr. Moriyo Kimura stated in a television commentary on April 25, two and a half months ago, that “COVID-19 is now airborne.” At a regular press conference on July 7, the WHO finally acknowledged the possibility of airborne transmission. Regarding the route of infection, 239 experts from Europe, the United States, and other countries published an open letter on July 6, citing cases such as “cases in Chinese restaurants where infection spread among customers at different tables from infected people,” citing the “possibility of airborne transmission of the new virus,” and calling for the WHO to review its countermeasures. It’s hard to deny that the WHO’s response has been slow to act.
2. Is herd immunity inevitable until a vaccine or treatment is developed?
(1) What is herd immunity?
“Herd immunity” refers to the indirect protective effect that occurs when a large proportion of a population is immune to an infectious disease. It serves as a means of protecting those who are not immune.
In a population where a large number of people are immune, the chain of infection is more likely to be broken, and the spread of the disease will be contained or slowed.
The higher the proportion of immune people in a community, the less likely those who are not immune will come into contact with infected people.
(2) Is herd immunity inevitable?
If COVID-19 is airborne, it appears that the spread of infection cannot be stopped by simply “suppressing cluster infections by tracing infection routes,” “avoiding the three Cs,” and “self-restraint on going out” until a vaccine or treatment is developed.
If that is the case, is the only way to contain the disease the need to achieve “herd immunity,” in which 60-70% of the population is infected?
By the way, during the “Spanish flu” in Japan (with a population of approximately 55 million at the time), the infection rate was 42%, and approximately 450,000 people died.
3. The Difference Between “Droplet Infection” and “Airborne Infection”
(1) Droplet Infection
Infection occurs when droplets containing pathogens, such as nasal mucus, saliva, and phlegm, are dispersed by an infected person’s cough or sneeze and land on mucous membranes. Droplet infection occurs within the droplet’s range, and the risk of infection varies depending on distance, time, and the presence of obstacles. Increasing the distance, shortening the contact time, and creating obstacles can reduce the risk of infection.
In essence, droplet infection is an infection route that occurs when droplets are directly inhaled from the cough or sneeze of an infectious disease patient.
The droplet dispersion range depends on weather, wind direction, and other conditions, but generally, infection can occur if a person is within 2 meters of the droplet for approximately 30 minutes.
Infectious diseases transmitted through droplets include influenza, rubella, mumps, whooping cough, mycoplasma, colds (rhinovirus, adenovirus, etc.), and respiratory syncytial virus (RSV).
(2) Airborne Infection (Droplet Nucleus Infection)
Airborne infection differs from droplet infection. In airborne infection, after the water in droplets released by coughing or sneezing evaporates, only very small pathogens (less than 5 μm in size) become “droplet nuclei” and remain suspended in the air for a long time, infecting anyone who inhales the air. Infection can occur even if you are more than 2 meters away, have a screen, or enter the same room after the infected person has left.
In essence, airborne infection refers to the “transmission route caused by inhaling airborne pathogens.”
Traditionally, airborne infectious diseases were considered to be tuberculosis, measles, and chickenpox, but it appears that “novel coronavirus pneumonia (COVID-19)” is also spreading via airborne transmission.
(3) Summary
Airborne and droplet infections are both caused by pathogens contained in droplets. Airborne infection occurs when the water in droplets evaporates, causing pathogens to float in the air and be inhaled. On the other hand, droplet infection occurs when droplets themselves enter the mouth or nose.
Both methods of infection may seem similar. However, airborne pathogens float in the air as extremely small “pathogens themselves,” measuring less than 5 μm. This makes them a frightening route of infection, as they can infect people who are not nearby or who just happen to be passing by.
In contrast, droplet infection can only spread to people within a 2-meter radius when a person coughs or sneezes. The risk of infecting an unspecified number of people is much higher with airborne infection.
(4) Aerosol Infection (Confined Space Infection)
The term “aerosol infection” has become increasingly common recently, but it is not a technical term.
Aerosols refer to particles smaller than droplets. They are somewhere between “droplet infection” and “airborne infection,” and are used to describe infections occurring in “enclosed, confined spaces” such as medical examination rooms or taxis.
4. Differences between PCR Tests and Antibody Tests
(1) PCR Tests (Polymerase Chain Reaction Tests)
① Purpose/Characteristics: Determines whether the virus is currently present in the body.
② Collection Method: Nasal swab taken from the back of the nose.
③ Sample Collector: Because samples must be collected from a precise location, they are performed by specialists (healthcare professionals).
④ Time to Results: Several hours.
⑤ Accuracy: Good.
(2) Antibody Tests
① Purpose/Characteristics: Determines whether a person has been infected in the past.
② Collection Method: Blood collection.
③ Sample Collector: Like many test kits, self-collection is possible.
④ Time to Results: Approximately 10-20 minutes.
⑤ Accuracy: Lower than PCR-based tests.
(3) Summary
PCR tests can determine whether the virus is currently present in the body (whether the person is infected).
In contrast, antibody tests can determine whether a person has been infected in the past, their current state of infection (is it in the early stages of infection, or has some time passed since infection) and whether they have already acquired the ability to resist the virus (antibodies) (i.e., whether they are less likely to infect others).