It can be said that without group immunity, almost all animal populations cannot continue. However, during the COVID-19 epidemic, this ubiquitous natural phenomenon was discredited in China, and even distorted as deliberately infecting most people with COVID-19 and establishing group immunity. Some people even say that group immunity can only be established through vaccination, and there has never been a successful precedent for establishing group immunity through natural infection. Then I want to ask, who established the group immunity of wild animal populations to certain microorganisms by vaccinating them? How did the plague end? Any plague, no matter how vicious, which is difficult to block the route of transmission, will eventually succumb to human immunity, including all animal populations that have not yet become extinct. The difference is that the cost of establishing group immunity is different, and the worst may be that the population is ten to seven or eight and the rooms are nine empty. But no matter how much sacrifice, the group immunity established among survivors will keep microorganisms out of the crowd and form an ecological balance. When this balance is broken, there will be a new epidemic and a new ecological balance of group immunity will be established. Below, we might as well explain some famous plagues in recorded European history.
Justinian plague This is a plague epidemic caused by Yersinia in Constantinople, the capital of Byzantine Empire. It is believed that Yersinia pestis was brought to Constantinople from rats in grain offerings of conquered Egypt. The plague led to the demise of Constantinople, where it is said that few people survived. The plague spread like wildfire to Europe, Asia, North Africa and Arabia, and it was estimated that about 30 million to 50 million people died, accounting for about half of the world population at that time. No one knows how this extinct plague ended. From the point of view, it can only be the result that some people survive in some way during the epidemic, and the survivors establish a high coverage of group immunity to achieve ecological balance.
The Black Death, another plague epidemic in Europe, Yersinia pestis is the same as those microorganisms that cause human infectious diseases. Although the human population immunization suggested that it be expelled from the human community, it was infected in not fade away (except smallpox virus). 800 years after the epidemic that killed half the world's population, it made a comeback in Europe, forming an epidemic called the Black Death. It is believed that the epidemic that swept through Europe killed one third of the population in Europe at that time. The only difference is that this time people learned an epidemic prevention trick, that is, knowing that isolation between people can prevent fleas from spreading diseases. In other words, the end of the epidemic is the result of both isolation and group immunity.
During the Great Plague or Black Death in London, people learned to isolate this epidemic prevention measure, which led to some people not being infected, so the established level of group immunity was not enough. This low level of group immunity led to Yersinia pestis never being expelled from the human community. After the Black Death epidemic, the plague has never stopped, and there will be an epidemic, with a total of about 40 epidemics. It is believed that every epidemic in London will lead to the death of about 20% of the population.
Until the biggest outbreak in years broke out again in London. At that time, there were two measures to end the epidemic: isolation and group immunity established by universal infection.
Eliminating the smallpox epidemic in the "New World" is an ancient infectious disease in the "Old World" in Asia, Europe and Africa. A large-scale epidemic will cause about 30% of the infected people to die (the mortality rate is 30%), and the survivors will leave lifelong scars (these scars on their faces are called "pockmarked" in China) and get lifelong immunity.
Due to the persistent epidemic, people in the old world maintained a certain level of group immunity, thus establishing an ecological balance between smallpox and human beings on the basis of this low level of group immunity.
With the "discovery" of the "New World" by European navigators, this rather "mild" old world plague was brought to the New World. As a result, an epidemic of population extinction eventually formed a new continent. It is believed that the smallpox epidemic in the New World led to the extinction of 90% to 95% of the indigenous population in Mexico and the United States, and the total population decreased from 1 1 10,000 to 1 10,000. The reason is that the new world population has never been exposed to the "mild" virus of the old world, and the group immunity level of the population is 0%. Of course, as a "reward", syphilis in the New World was also brought to the Old World, causing a considerable epidemic.
Cholera in Britain-The Victory of Public Health Research Cholera has been plaguing Britain, causing a large number of deaths. Because the occurrence of the disease is related to contact with the Thames, people at that time thought it was caused by miasma produced by the river. Later, scientists triggered a deadly outbreak of infection, and people got sick by drinking water from street wells directly. After hard work, the authorities were persuaded to dismantle the pumps of these wells, and cholera was miraculously contained, which was also the beginning of establishing clean drinking water for public health. In other words, the end of cholera does not depend on group immunity, but on the blocking of transmission routes.
Group immunity is the only end point that it is difficult to stop the spread of the epidemic. Some people say that due to the protection of Chinese medicine, there has never been a major plague in the history of our country. Actually, this is a misunderstanding. It is not that there is no plague epidemic in China, but it lacks detailed records. According to the detailed history of plague in Europe, four of the five pandemics ended with the establishment of group immunity. The only exception is the cholera epidemic, because its transmission route is food-borne diseases transmitted through drinking water, and its prevalence in the population is limited, which will not cause universal infection. For epidemics that are difficult to block the route of transmission (such as respiratory infectious diseases and insect-borne infectious diseases), as long as a high level of group immunity cannot be established, it is usually difficult to really end the epidemic. For example, even if malaria is infected, it is difficult to establish long-term immunity, and it is impossible to establish group immunity in the population. This is the reason why malaria is repeatedly prevalent in epidemic areas. Of course, since even infection cannot establish immunity, it is naturally difficult to develop a vaccine.