SARS-CoV-2 will become one of the common coronaviruses colds by the end of 2020 in the northern hemisphere.

What's happening now is not the second wave of the pandemic, but CASEDEMIC.


As everybody noticed, the COVID-19 pandemic is already over in the northern hemisphere. What is happening now is not the second wave of the pandemic but casedemic; only cases can increase while deaths or severe cases keep declining. 


Here is a Tokyo version of casedemic. The situation has changed since the end of June; more cases (with more testing) but less deaths.

I have calculated 7-day moving average of case-fatality-ratio for Tokyo and West Europe countries and found that CFR has dropped to one-tenth to one-twentieth of the first wave in April.


Why has the CFR changed drastically? It is not because of the weakening of the virus but our T-cell memories the virus.


Some people attribute this casedemic phenomenon to the weakening of the virus.

I don't think it's correct. The countries which had suppressed the initial wave by the early and draconian way such as Australia, Israel, Hong Kong, etc. have seen the second wave with the same high CFR. 


The following two reasons can explain why and where the pandemic has changed to the casedemic.
  1. Those who were very vulnerable died in the first wave
  2. Our T-cell memories SARS-CoV-2 and gains immunity 
The first reason would be easy to imagine and understand for everyone.
I'll cite some papers explaining the second reason.

Robust T cell immunity in convalescent individuals with asymptomatic or mild COVID-19
画像

Look at the above figure. Most of the people who were not infected but just exposed have gained SARS-CoV-2-specific response!

The papers below are worth reading.

Robust T cell immunity in convalescent individuals with asymptomatic or mild COVID-19
https://www.cell.com/cell/fulltext/S0092-8674(20)31008-4

SARS-CoV-2 T-cell epitopes define heterologous and COVID-19-induced T-cell recognition

SARS-CoV-2-specific T cell immunity in cases of COVID-19 and SARS, and uninfected controls

The last paper reveals that all the people who were infected with SARS in 2003 (n=23) still has the SARS-specific T cell immunity after 17 years! This indicates that our SARS-CoV-2-specific T cell immunity can last for a long period.


(BCG vaccination strengthens T cell immunity.)

Though the BCG hypothesis is not that relevant in this post, let me add the relation between T cell and BCG vaccination. I wrote the post below in May. I feel my prediction has come true.

Don't care about antibodies. Let's care for innate immunity; T cell and macrophage.

I cited the two papers in the above post. The latter paper is not about human but mice, but let me assume this applies to human as well.

Mycobacterium bovis BCG Vaccination Induces Divergent Proinflammatory or Regulatory T Cell Responses in Adults

Memory T Lymphocytes Generated by Mycobacterium bovis BCG Vaccination Reside within a CD4 CD44lo CD62 Ligandhi Population

In plain words, I would say as below. I hope scientists prove this in the near future.
  1. BCG vaccination levels up the baseline of T cell immunity
  2. BCG vaccination strengthens T-cell memory


A common coronavirus OC43 made its debut in 1889-1890 and killed around 625 per 1 million.

So, what future can we foresee?
Let's look back at our history to foresee the future.

I found a very interesting history of the common coronavirus; OC43.

There was a pandemic in 1889-1890 which killed 1 million people and it was thought that an influenza virus caused it. However, recent studies say that the virus might have been not actually an influenza virus, but human coronavirus OC43.

1889–1890 flu pandemic

When the human coronavirus OC43 made its debut in 1889-1890, it killed 1 million people, which were around 625 deaths per 1 million population at that time. This death rate is a similar range of COVID-19 death rate among the countries where BCG vaccination is not compulsory. This is a coincidence but indicates that it's a good historical reference.

The 1889-1890 pandemic had continued for a few years but I think this COVID-19 pandemic will ends sooner, maybe in a year or so, because we are living in a global economy.

There is a great article about this on Bloomberg. 

Our Coronavirus Predicament Isn’t All That New

Do we fear the human coronavirus OC43 now? Do we PCR test OC43 infection and isolate them? Do we vaccinate ourselves against OC43? Do we acquire or care about the herd immunity against OC43? You know the answers to these questions. We'll get infected with SARS-CoV-2 again and again but the probability of becoming severe has been decreasing dramatically.


(Rushing to a new vaccine may be riskier than getting infected with SARS-CoV-2. The old BCG vaccine would work.)


I am worried about the rush to the new vaccines and think that exposing to the real virus may be at a lower risk than taking the new vaccines which cause side-effects among the healthy young samples. If it is a success, it's a novel prize invention because it means that we find a way to prevent a cold.

I believe BCG vaccination is much safer and quite effective. Please check the result from a UAE hospital.

SARS-CoV-2 will become one of the common coronaviruses colds.

Once we expose ourselves to SARS-CoV-2, our immunity such as T cell memories it and SARS-CoV-2 will become a common coronavirus cold. I think this is already happening in most of the northern hemisphere and will happen in the southern hemisphere.

Also, some people worry about the seasonality of SARS-CoV-2 but I don't worry much about the seasonality as it prevailed in summer or winter and the speed is not that different. It looks 1.5 times faster/infectious in winter from Australia data. In other words, getting infected in summer is better than in winter as the curve is less steep. Israel decided to abandon its suppression strategy and spread the virus this summer. I think it is a smart move. 

SARS-CoV-2 will become one of the common coronaviruses colds by the end of 2020 in the northern hemisphere. 

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