Vaccine refers to vaccine-preventive biological products used for human vaccination in order to prevent and control the occurrence and spread of infectious diseases. A biological product refers to a preparation for prevention, diagnosis and treatment prepared by using a microorganism or a toxin thereof, an enzyme, a serum or a cell of a human or an animal. Biological products for vaccination include vaccines, vaccines and toxoids. Among them, the vaccine is made of germs; the virus, rickettsia, and spirochetes are vaccines, sometimes collectively referred to as vaccines.

The principle of disease resistance of vaccines is to automatically prevent pathogenic microorganisms (such as bacteria, rickettsia, viruses, etc.) and their metabolites by artificially attenuating, inactivating or using genetic engineering methods to prevent infectious diseases. Immunological preparation. The vaccine retains the characteristics of the pathogen to stimulate the immune system of the animal. When the animal is exposed to this non-invasive pathogen, the immune system will produce certain protective substances, such as immune hormones, active physiological substances, special antibodies, etc.; when the animal is exposed to the pathogen again, the animal's immunity the system will follow its original memory and create more protective substances to prevent the damage of pathogens.

How is the vaccine classified?

The types of vaccines are live vaccine, dead vaccine and toxoid. Has the following characteristics.

Live attenuated vaccine: A live attenuated vaccine is used as a vaccine. Such as polio, poliomyelitis, measles, BCG (BCG) and so on. If a live vaccine is inoculated, a slight infection will occur and the resistance between the blood and the cells will increase. Immunity lasts for a long time, so there is no need to perform several additional immunizations.

Inactivated vaccine: Kill the pathogen and leave only the toxin that produces immunity as a vaccine. Such as whooping cough, Japanese encephalitis, influenza, and so on. Inoculation of inactivated vaccines can produce antibodies in the blood to kill invading pathogens. Inactivated vaccines cannot proliferate in vivo like live vaccines, so it is necessary to vaccinate frequently to boost immunity.

Toxoid: removes the toxins of the pathogen and weakens the toxicity to become non-toxic. When a toxin is selected, a substance can be produced in the blood to make the toxin in the bacteria non-toxic, thereby preventing disease. Diphtheria and tetanus vaccines fall into this category. However, like the inactivated vaccine, it is not sustainable, so it is necessary to vaccinate frequently.

Vaccines can be classified from active and passive immunizations, artificially active (inactivated vaccines, live attenuated vaccines, toxoids) and artificial passive immunizations.

Inactivated vaccine: use immunogenic bacteria, viruses, rickettsia, spirochetes, etc., artificially cultured, and then killed or killed by physical or chemical methods. This vaccine loses its ability to reproduce but retains its immunogenicity. After the dead vaccine enters the human body, it cannot grow and reproduce, and the stimulation time of the body is short. To obtain long-lasting immunity, it is necessary to repeat the vaccination several times, that is, vaccination.

Live attenuated vaccines: Live vaccines or live attenuated vaccines are prepared by artificially directed variation methods or by screening live microorganisms that are less virulence or substantially non-toxic. Common live vaccines include BCG (TBG), measles vaccine, polio vaccine (polio). After inoculation, it has the ability to grow and reproduce in the body, close to natural infection, which can stimulate the body's long-lasting immunity to the pathogen. The live vaccine is used in smaller amounts and the duration of immunization is longer. The live vaccine has a better immune effect than the dead vaccine. For example: varicella vaccine is a live attenuated vaccine, leprosy, mumps vaccine are all live vaccines.

Toxoids: Exotoxins lose their toxicity after being treated with formaldehyde, and remain immunogenic, which is a toxoid. Adding appropriate amount of aluminum phosphate and aluminum hydroxide to form a refined toxoid. Slow absorption in the body; can stimulate the body for a long time, produce higher titer antibodies, enhance immune effect. Common toxoids are diphtheria toxoid and tetanus toxoid.

Artificial passive immunization: anti-toxic, human immunoglobulin preparation, cytokine preparation, monoclonal antibody preparation.

Both artificial active immunization and artificial passive immunization can increase the body's ability to resist disease, but the duration of the latter is short, mainly with treatment and emergency prevention.