Zhong Nanshan talks about group immunity. What is group immunity?

Group immunity (group immunity) refers to the resistance of people or herds to infection. The high level of immunity in the population indicates that the proportion of animals with anti-infection ability in the population is high. Because the possibility of epidemic disease depends not only on the number of resistant individuals in the animal population, but also on the contact frequency between individuals in the animal population. If 70%-80% of the animals in the population are resistant to drugs, there will be no large-scale outbreak.

There are two meanings about biological population: population genetics refers to the genetic composition of the population, that is, the frequency of genes and genotypes appearing in the population. Pure line varieties are homogeneous in population and homozygous in individuals; However, the population of open pollinated species is heterogeneous and individuals are heterozygous. The study of population genetic composition in crop breeding is helpful to the decision-making of breeding scheme. In crop cultivation, the composition of a single crop population planted in the same field is opposite. This group may be composed of several crops, such as mixed sowing, intercropping or monoculture. Studying the space occupied by each individual in the population, the composition of its phenotype and the dynamic coordination among individuals will help guide the high-yield cultivation of crops.

Group immunity refers to people's ability to resist the invasion and spread of infectious disease pathogens, which is reflected in the proportion of people with immunity to the whole population. When most people in a group are immune to an infectious disease, they will not get sick, and group immunity will provide indirect protection for those who are not immune.

Therefore, when the proportion of immune population in the population decreases, that is, when the immunity of the population decreases, the susceptible population will increase greatly, and the incidence of infectious diseases will increase accordingly; When people's immunity is enhanced, the number of infected people decreases, and the possibility of susceptible people being infected also decreases, thus reducing the incidence of infectious diseases. Group immunization does not apply to all diseases, but only to infectious diseases (diseases that can be directly transmitted among people).