1. What is group immunity?
This refers to the phenomenon that infectious diseases cannot spread when more than 90% people in a group are immune. This is actually easy to understand, because the time for an infected person to cure or die is limited. If the disease is not transmitted to the next person within this time, the transmission chain will be interrupted. Every contact between patients and others is like a lottery game. If only 10% people can be infected, it is very likely that 10 people will not win 20 games in a row, and the spread chain of germs will not be maintained, let alone increased. The disease will disappear naturally.
Second, how to make 90% people immune?
Two schemes:
Before human beings invented vaccines, they mainly relied on natural selection. Because of the diversity of genes, naturally some people can resist pathogens or have strong immunity, and can overcome diseases through adjuvant therapy. When there is an epidemic, some people will die, some people will survive through painful struggle, and a few people will easily defeat pathogens.
Then, in the case of population reduction, the per capita resource richness will naturally increase, creating conditions for population rebound. Those who can survive the great plague, especially those who sacrifice less, will have an advantage, that is, "survival of the fittest" in natural selection. When the proportion of people who have been infected with immunity and innate immunity is getting higher and higher, the spread of pathogens will become more and more difficult and the epidemic will gradually recede.
When human beings invented vaccines, they could get immunity almost painlessly by vaccinating everyone. When the vaccine coverage rate reaches nearly 90%, infectious diseases will gradually disappear.
Third, what is the difference between the two?
The biggest difference is the high cost of natural selection. Take smallpox virus, a notorious virus in human history and the first virus completely eliminated by human beings, as an example. According to different strains, this virus has three mortality rates: 1%, 30% and 97%, and nearly 300 million people have been harvested by smallpox. It was in this bitter struggle that the British doctor Edward Chennault invented the vaccinia vaccine. Humans only need to be infected with almost harmless bovine smallpox virus to gain immunity to human smallpox virus. Through the popularization of vaccinia, it took only 1.83 years for human beings to completely eradicate smallpox that has ravaged the world for more than 3000 years.
If there is no vaccine, how long will it take for human beings to completely defeat smallpox? Let's take an example from the animal kingdom: In order to eliminate the rabbits that are rampant in Australia, the Myxoma virus was introduced, and the mortality rate was as high as 99.8%. At the peak, 80% of the 654.38+000 billion rabbits were eliminated!
But this 0.2% is the fire of the rabbit's counterattack. Rabbits have the highest reproductive capacity among mammals. The mother rabbit has two wombs and can give birth to six fetuses a year, with at least four fetuses each. Under such a powerful iterative effect, the number of rabbits began to rebound in less than 20 years. At present, only about 40% rabbits in Australia will be infected with rabbit myxoma virus.
Humans usually give birth to one child a year, reaching the reproductive age 18 years. Although COVID-19 is not as deadly as smallpox or rabbit myxoma virus, it is still not good to establish natural immunity.
Most importantly, people are not numbers on paper. To establish natural immunity, it is necessary to "destroy" some lives. The population of Britain is 66.49 million. Even considering the progress of vaccine development, about 65,438+0% people in COVID-19 died directly from infection. What is the concept of 600 thousand people? When we do broadcast gymnastics in our primary school, the whole playground can probably stand 1200 people. To fill so many people, we need a full 500 playgrounds with an area of 1 1 Tiananmen Square! Can Britain really afford this price?
Civilization is a powerful force higher than one dimension.
Man is the body of an animal, but it has the dimension of civilization. After billions of years of long evolution, we are fortunate to be the only intelligent creature that has broken through the ceiling of evolution and entered a higher dimension. The evolution of civilization is much faster than the change of genes, and the evolution of traditional creatures has long been a force to promote human progress; In the near future, the power of science will reverse optimize genes, so that we can have a perfect biological body without cruel natural selection.
Fighting against natural disasters with flesh and blood and promoting evolution with death is an backward thinking mode of giving snipers a shot and smashing walnuts with a cooking machine. Civilization is the inevitable product of evolution and the supreme power of a higher dimension. Fortunately, human beings are in the civilized world, so it is natural to confront disasters in a civilized way, instead of pinning their hopes on the "Renaissance".