Covid-19 Japan case; Low severity and mortality

No one expected Covid-19 pandemic when 2020 was started. I personally, plan to held a wedding party to invite friends all over the world. However, of course, I had to postpone it to next year. The world, including Japan, still chaos and uncertain due to the disease since we can't expect when a pandemic will be controlled and be backing to normal life. Should we wait for vaccine release?

It's controversial if Tokyo will be like NY in US, we won't face second or third wave. I read one article written by a doctor to describe and explain a reason with fact-fullness. So that I would like to introduce it in English since there is less chance to be read by a foreigner in English.

The number of people who test positive for the Covid-19 is increasing, mainly in Tokyo. On the 15th of July, Tokyo raised the alert level to the most serious of the four-level, " it seems that infection is spreading". However, there are many symptomatic and mild cases, and even experts say that there is a different opinion on whether to raise the level. In addition, the number of people who died of Covid-19 is less than 1000 which is only one-third of the annual influenza death. There is a big gap between the prediction of an outbreak in Japan and the actual damage situation in Western countries. 

The big difference between the new Coronavirus and influenza. Some Japanese expert predicts that the death toll will rise 10,0000. However, the doctor says the number of increase is only the people who have detected a PCR positive by PCR testing, not the number of infected people to saying exactly. Of course, it is not the number of people affected. Especially in young people, PCR-positive people are unlikely to develop, and many cured with no symptoms or minor symptoms. In addition, the prediction that "hundreds of thousands will die" believe the wrong premise of Covid-19. Based on the facts, he created a model that can see the whole picture and quantify it, which is the stage 7 infection model. The infection stage of Covid-19 is divided into seven stages from stage zero to stage six.

The coronavirus is a mild virus from the early stages to the middle stages, although it has high exposure, but leak infection and toxicity. But also in many cases, it's a mild virus that ends asymptomatically or just cold. However, it causes a situation such as a cytokine storm and thrombus formation, and causes serious disorders in multiple organs, mainly to lungs among elder people. And then, such people end in death. 

in general, a characteristic of a virus is it's less virulent so that it can't be found in the human body. Therefore unless it grows in a certain amount, an antibody against the human body can't have proceeded. On rare occasions, the host's human body may be alerted and killed.

The initially disseminated expectation that hundreds of thousands of people would be killed in each country including Japan, but it's far off. The reason seems that people refer influenza base model. and there is a big difference between the two models. When a pathogen enters the body, innate immunity* are generated. It takes several days for acquired immunity** to start producing antibodies. *Innate immunity; The mechanism of the body that detect and eliminate invading pathogen. **Acquired immunity; The mechanism that it's recognized other pathogen and remember. So that once the same pathogen enter are recognized in a body, it's eliminated. 

In the case of influenza, the virus is highly toxic and you will soon have an obvious symptom such as nasal discharge, cough, myalgia, and fever. Since the virus rampage in the body very actively, the human body has to immediately react ordering activation of antibody. Therefore, if the antibody test was taken, the result would be positive. In many cases, the human body suppresses a virus by the acquired immunity and cure it in a short period such as from 1 to 10 days. However, sometimes it fails and caused pneumonia and then death. How about Covid-19? According to "Interpretation of a diagnostic test for the new corona" published by JAMA online, it takes much time to activate antibody for Covid-19. Why? The body considers the virus to be sufficient to treat with natural immunity rather than creating an antibody because the toxic level is very low. But also, in fact, natural immunity treat and cure Covid-19. 

A research team interprets a phenomenon of the virus is considered to be sufficient to treat with natural immunity rather than producing an antibody in your body because the Coronavirus is less toxic. In the general case, natural immunity treat and cure the coronavirus. In such a condition, a person is asymptomatic or have a light flue symptom without knowing he/she are infected by the new coronavirus. If PCR test is performed during the period, the test results if it's positive because the virus is in the body. On the other hands, since antibody are not produced in the body, the antibody test will naturally be negative. And then, even if symptom proceeds and acquire immunity activate, a cytokine storm may occur among a small number of people who could not suppress the coronavirus and may dead. Antibody test shows a different perspective among big city all over the world; 16.7% for London, 12.3% for New York, and 0.1% for Tokyo. If we consider the number based on the influenza model, we interpret that Tokyo could prevent much death. However, Tokyo will fail to preservation next time if implement the right counter-attack since Tokyo still doesn't have the antibody. 

Since the Japanese government didn't ask strong lock-down as European governments did, it's unlikely that exposure to Coronavirus for Japanese people are smaller than for European. Based on the hypothesis, maybe people have already infected by the new Coronavirus, but most of them are cured by natural immunity. It is cured before an antibody is formed. It's more mature logic to explain the current situation happen in Japan, referring to the hypothesis. Even if the second wave surges new cases in Japan, it's going to be less impact than in Western countries because of such natural immunity strength of Japanese people. 

It's a limited date to predict the new Coronavirus contagion model, such as death rate, mortality. By using the hypothesis of data; the Japanese population, the number of infected cases by age group and estimated antibody positive rate, referring to the University of Tokyo and Kobe Municipal hospital. The simulation shows the following results. First of all, 30 -45 % of the Japanese population have already infected. Then 98% of infected people are an asymptomatic or light symptom. 2% feel cold and are cured by acquired immunity. In that 2%, five people out of ten thousand aged groups 1*, three people out of 10,000 people at aged group 2**, 1.5 people out of a thousand at age group 3*** and three people out of a thousand at age group 4**** are escalated to serious condition. 
* from 20 years old to 30 years old
** from 30 years old to 59 years old
*** from 60 years old to 69 years old
**** over 70 years old

Based on the series of argument. we try to explain a reason why the death rate is one hundredth comparing with European countries' damages with some hypothesis. Firstly, it's regarding the infection rate. it can be assumed that the infection rate in Japan, especially among elder people, are much less than in European countries. There are a protocol and acknowledgement among society to prevent elder people from disease. For instance, nursing houses forbidden family to meet during a flu season in the winter. So the hypothesis of infection rate among elder people in Japan set at 10% but 40% in European countries. Secondly, we assume that Japanese (or Asia pacific people) are a higher ration to be cured by natural immunity than European. It's most probably due to either Japanese or Russian BCG. If natural immunity is standard divination, mortality ration in infected people would be 2%. It's quite similar number as we've seen in actual cases in Japan. Contrary, 98% of infected people in Japan end up asymptomatic. As a consequence, contagion risk is quite low since 98% of Japanese are cured by natural immunity before infected each other. Moreover, it's only chance to be infected if you exposed with huge amount of infection. While, looking into antibody positive ratio in European countries, most of European can't be cured by natural immunity. a mortality ration of European would be 10% which is five times higher than Japanese. if we assume natural immunity ration in Japan is 2% and 20% in Europe, the small gap would lead large different to reproduction number as below chart; natural immunity ratio is described on horizontal. Since 20% of people can't cured by natural immunity, the case are increased with quadratic function formulation. 

Thirdly, it's assumed death rate among infected people is much less than European. The reason is simply it's higher probability among European to have blood clot than Japanese due to biological difference. Death ration among infected people is 0.01% for 0 to 69 years old Japanese, 0.4 15 for over 70 years old Japanese, while 0.05% for 0-69 years old European and 2% for over 70 years old European. That number is almost the same as the actual date as of today. As a result, it's most probably the death rate among Japanese are 100 times less than in European countries. 

On the other hands, let's discuss PCR test strategy and itself. PCR test can detect whether new coronavirus gene is in a body or not, which means that PCR can even identify Coronavirus which has no risk to infect people. Even a person who can cure the virus by natural immunity can possibly positive on PCR test. However, it's much less chance to infect virus to people because it's cured by themselves. That's why PCR test and the number of infected people by PCR can't be simply diameter to assess contamination status.

Therefore, we can conclude that more than 3800 people won't die of the Coronavirus in Japan unless the virus toxic character won't change. Moreover, we have to aware of social impact due to the knockdown, restriction, stay home and so on. Currently, the suicide rate in Japan increasing than the death of Corona. For students, they can't go to the classroom to learn, discuss and enjoy social due to the restriction. This is a more critical issue in our society. 

According to data, each country should have a different countermeasure to tackle the virus. For Japan, we don't need to push restriction for social activity, but much better to back to normal life. Otherwise, it cost our life due to nothing.