Whether the epidemic can be controlled depends on the speed of epidemic spread. The value of basic reproductive number R0 is often used to describe the spread speed of epidemic diseases, which can reflect the potential and severity of infectious diseases.
Basic reproductive number (R0): refers to the average number of patients who can be infected in an environment with all susceptible people without intervention. To put it bluntly, it is the average number of people a patient can infect under the condition of free transmission. This number will be greater than 1, if it is not greater than 1, the disease will not spread, it is a weak chicken disease and will be eliminated in evolution.
Effective regeneration number Rt: With the increase of prevention and control interventions (such as isolation of patients in shelters, isolation of individuals at home, wearing masks, etc.). ), or susceptible people have been sick or died in large numbers (such as the Black Death in ancient Europe). In the process of disease spread and development, the average number of people infected by a patient at time t.
R0 refers to the basic reproductive number, indicating the number of second-generation cases that can be infected under ideal conditions when a case enters the susceptible population. If R0 is greater than 1, then this infectious disease can spread in the whole population; Infectious diseases with R0 less than 1 tend to disappear. See the figure below. R0 can be used for epidemic situation analysis and judgment.
When R0 is greater than 1, infectious diseases can spread throughout the population in a limited time.
At different stages of the disease, R0 will change due to the virulence change of the virus itself (which may be weakened in future generations), or the structural changes of S (susceptible person), E (infiltrator), I (infected person) and R (drug-resistant person) in the population after a certain period of time, or manual intervention, such as vaccination, isolation and sanitary measures. Generally speaking, the value of R0 is between 2.2 and 3.5.
There are many methods to calculate R0, which can be roughly divided into two categories: one is to directly give the formula of R0 through mathematical derivation, and directly calculate the value of R0 according to the existing data; There is another model, which takes R0 as a parameter of the model, and then estimates the parameters according to the data.
Establish a model to solve R0 as a parameter:
The above is a basic SEIR model and its main symbolic significance. All researchers are based on this model. Statically, it is mainly set from the aspects of warehouse setting, randomness, crowd and spatial heterogeneity. For example, consider different age structures. Dynamically analyze and extract two basic features, namely, the dynamic expression mode (explicit expression and implicit expression) within subgroups and the coupling mode (full connection, local interconnection and network structure) between subgroups, such as whether the contact mode is nonlinear (structure extraction), so as to obtain different models. Through the study of SEIR model, we can predict the epidemic situation, the maximum peak and the number of infected people in a closed area, but obviously no area is closed, so we should regard each area as a node of the graph, and the flow between areas can be described by Markov transition, and run SEIR model for each node separately.
To prevent and control infectious diseases, it is necessary to reduce the effective regeneration number Rt to below 1 through various measures. Through effective intervention and prevention and control measures. The basic reproductive number is the most important parameter in epidemiological dynamics, which can not only describe the uncontrolled internal transmission ability of an infectious disease, but also serve as a reference for public health policies and set the target of how much prevention and control is needed. As the general public, we should contact people less, wear masks and minimize public transportation, so that we also contribute to reducing the effective regeneration number Rt to below 1.
All the research is aimed at fighting the epidemic. I hope the conclusion can effectively help the government to make decisions, so that ordinary people can effectively and rationally restrain their behavior after understanding the basic principles.
Now the people in Wuhan and Hubei are all our compatriots and belong to mankind. Coronavirus pneumonia is the enemy, they are not! Please respect and care for them!