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How can the new coronavirus become “influenza” and coexist with humans for a long time? The plague more than 100 years ago…
How can new coronavirus become “influenza” and coexist with humans? Is it feasible for humans and viruses to coexist?
Is “coexisting with the virus” feasible? , Coexistence with the virus may be difficult to achieve. For this question of “coexistence possible or not”, we can look back at the history of mankind and find out whether there has ever been a “new coronavirus” coexisting with mankind in the history of mankind. Coincidentally, there may be one such example.
We all know that the culprit of the COVID-19 epidemic is the “new coronavirus.” Since it is “new”, it must also be “old”, and the so-called “old type of coronavirus” except SARS in 2003 actually refers to the four types that have spread widely in the population before the epidemic that can cause colds. Of human coronaviruses: 229E, OC43, NL63 and HKU1.
What is interesting is that in the study of the coronavirus after the SARS epidemic in 2003, scientists found that the cold coronavirus HCoV-OC43 was likely to be the culprit of the influenza pandemic from 1889-1890. The epidemic more than a hundred years ago was also known as Russian Flu. It is estimated that the epidemic that swept the world was likely to cause the deaths of more than 1 million people in the world at that time, and the case fatality rate (CFR) was estimated at 3 Range from %~8%.  We must know that at that time there were only about 1.5 billion people in the world, and the average age was much younger than it is now. At that time, more than a million deaths from infections were probably equivalent to about tens of millions now. It can be said that it is a very powerful virus that can rival COVID-19.
1889-1890 Epidemic Map
Especially last month, a review published in Microbial Biotechnology detailed the clinical evidence that HCoV-OC43 was the pathogen of the 1889-1890 epidemic.  The evidence cited in the study included serum antibodies of patients of different ages in the early 20th century, molecular clock time into humans calculated by gene mutation rates, and clinical reports and symptom descriptions recorded by doctors during the epidemic at that time. In particular, the clinical symptoms described by the doctors at that time were very similar to the new coronavirus, but were quite different from other possible H2/H3 influenza virus symptoms. For example, patients at that time often had symptoms of multiple organs (respiratory symptoms, digestive system). Symptoms, neurological symptoms including loss of taste and smell), slow recovery and often long-term sequelae (Long-covid), multi-organ thrombosis, extremely high mortality in elderly patients, and almost no symptomatic infections in infants and children (flu The mortality rate of the elderly and children is very high).
Mortality of different age groups of the Spanish influenza and the influenza of 1911-1917
New coronavirus hospitalization/severe illness/mortality in different age groups
Seeing this, many people may have questions: If HCoV-OC43 is really the powerful virus behind the epidemic that caused millions of deaths from 1889 to 1890, then how did it become a kind of mild and relying on drinking hot water at the moment? What about the common cold virus that can heal itself?
One possible reason is that because HCoV-OC43 is very infectious, most of us have experienced at least one infection at a very young age. Because the OC43 virus has very mild symptoms for children, it is basically just a common cold. After almost everyone experienced such a cold in childhood, we have acquired immune memory of the OC43 virus. In addition, each time we have a cold caused by the OC43 coronavirus, the level of antibodies produced will gradually decrease over time. When the overall antibody level of the population drops to a relatively low level, the virus will cause waves of population cycles. spread. This has also been verified in a study of Nature Medicine found that the population’s antibodies to various cold coronaviruses have a cyclical change of about two years. 
Changes in the level of cold-coronavirus antibodies in the population over time
In other words, each of us will experience HCoV-OC43 coronavirus infections from a very young age in our life. Each infection will strengthen our body’s immune memory and let the body’s antibodies against it. Keep it at a certain level. In this way, even with age, the mortality rate of viral infections also increases, but due to the immune memory enhancement caused by long-term repeated infections when young, even at the dangerous advanced age, in most cases without vaccines and drugs, its infection is harmful For our bodies, it will only be a common cold.
Of course, although the HCoV-OC43 coronavirus and this new coronavirus are both RNA coronaviruses, there are considerable differences. For example, the receptor for the HCoV-OC43 virus to enter human cells is Neu5Ac, and SARS-CoV-2 is ACE2. Receptor. In addition, if we want to eventually become the endemic cold endemic that coexists with us, such as the current HCoV-OC43, rather than the potent and fatal pandemic, many conditions are needed:
■ The infectious force must be strong enough. Only with strong contagion can most people have the experience of infection and produce immune memory at a very young age when the symptoms are mild. Obviously, as in Wuhan, the original strain with R0 of about 2~2.5 may not be able to achieve, but the Delta strain, such as the mutant strain with R0 may be as high as 6 or more, may be able to meet this condition.
■ The vaccine is not strong enough and not effective for life. If the vaccine is very effective and effective for life, COVID-19 is likely to be wiped out or nearly wiped out by the vaccine just like smallpox and polio virus.
■ The level of immune escape caused by virus antigenic drift is relatively low. In this way, the neutralizing antibody produced by the body every time the immune memory is awakened will not lose too much due to virus mutation. The current research on the neutralizing antibodies of COVID-19 shows that although different mutant strains have certain antibody escape phenomena, in general, the neutralizing antibodies produced after infection recovery and vaccination are still relatively effective. Of course, if COVID-19 also has a flu-like antigenic shift that will cause a significant immune escape, it is likely that this condition will not be met, but I think people with relevant professional knowledge should be able to understand COVID-19 in principle. There is a clearer understanding of the flu-like antigenic shift.
■ The symptoms of repeated infections after multiple infections strengthen immune memory are mild enough. In this way, the symptoms of re-infection caused by reduced antibody levels always remain in a relatively mild state. However, due to the relatively short occurrence of the epidemic, there is a lack of sufficient clinical data to confirm or falsify whether COVID-19 meets this condition.
Of course, will the new coronavirus eventually become the next fifth cold coronavirus that is prevalent in human society like HCoV-OC43, or will it be successfully eliminated worldwide by vaccines or even non-drug interventions like smallpox? Virus, or has it become a virus model that has never been experienced in human history? The answer to this question I think we will be able to make a rough judgment based on the epidemic situation in the next year or two.
(source:internet, reference only)
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