What Is the Salk Vaccine?

Vaccines refer to biological products made from various types of pathogenic microorganisms for vaccination. The vaccine made with bacteria or Borrelia is also called vaccine. Vaccines are divided into live vaccines and dead vaccines. Commonly used live vaccines are BCG vaccine, polio vaccine, measles vaccine, and plague vaccine. Commonly used dead vaccines are pertussis vaccine, typhoid vaccine, meningococcal vaccine, and cholera vaccine.

The production time varies from vaccine to vaccine, and some vaccines can take up to 22 months to produce one batch. The development of vaccines is a long and complex process and is costly. Vaccination is the most economical and effective public health intervention to prevent and control infectious diseases. It is also an effective means for families to reduce the incidence of diseases and reduce medical costs.

It is estimated that immunizations can prevent 2 to 3 million deaths each year from diphtheria, tetanus, pertussis and measles. Global vaccination coverage (proportion of children worldwide with recommended vaccines) has remained stable over the past few years.

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2019-12-02 10:12 Implementation of China's first vaccine management law

On December 1, the "Vaccine Management Law of the People's Republic of China" came into effect. As China's first special law on vaccine management, the Vaccine Management Law has clearly stipulated in terms of vaccine development, registration, production, batch issue and circulation. ... more

Vaccine classification

Vaccines in China fall into two categories.

The first type of vaccine refers to vaccines provided to citizens by the government free of charge. Citizens should be vaccinated in accordance with government regulations, including vaccines determined by the national immunization plan, and vaccines added by the people's governments of provinces, autonomous regions, and municipalities when implementing national immunization plans, Vaccines used for emergency vaccination or mass vaccination organized by people's governments at or above the county level or their health authorities;

The second type of vaccine refers to other vaccines borne by citizens at their own expense and voluntarily.

Vaccine principle

Vaccines are autoimmune preparations used to prevent infectious diseases by artificially attenuating, inactivating, or using genetically modified methods for pathogenic microorganisms (such as bacteria, rickettsia, viruses, etc.) and their metabolites. The vaccine retains the characteristics of pathogenic bacteria that stimulate the animal's immune system. When the animal body comes into contact with this non-harmful pathogenic bacteria, the immune system will produce certain protective substances, such as immune hormones, active physiological substances, special antibodies, etc .; when the animal is exposed to this pathogenic bacteria again, the animal's immunity The system will follow its original memory to create more protective substances to prevent the harm of pathogenic bacteria.

Vaccine types

Vaccines are generally divided into two categories: preventive vaccines and therapeutic vaccines. Prophylactic vaccines are mainly used for the prevention of diseases, and the recipients are healthy individuals or newborns; therapeutic vaccines are mainly used for diseased individuals, and the recipients are patients.

According to tradition and custom, they can be divided into live attenuated vaccines, inactivated vaccines, antitoxins, subunit vaccines (including peptide vaccines), carrier vaccines, and nucleic acid vaccines.

Live-attenuated vaccine

Most of these types of virus vaccines are more than 90% effective, and their protective effects usually last for many years. Its outstanding advantage is that the pathogen replicates in the host to produce an antigenic stimulus. The quantity, nature, and location of the antigen are similar to natural infections, so the immunogenicity is generally very strong, and there is no need to strengthen immunity. This outstanding advantage is also potentially dangerous: infections can occur in some individuals with poor immunity; mutations may restore virulence. The latter can be more reasonably attenuated with the understanding of the molecular basis of pathogenic virulence, which may make its attenuation more definite and fail to restore virulence.

Inactivated vaccine

Compared with live attenuated vaccines, inactivated vaccines use non-replicating antigens (dead vaccines). Therefore, they are safe, but their immunogenicity is also weakened, and they must often be strengthened. It should be noted that not all pathogens can be highly effective vaccines after inactivation: some of these vaccines are highly effective, such as Salk's polio vaccine (IPV) or hepatitis A vaccine; others are inefficient, Short-term vaccines, such as inactivated cholera vaccines, have almost been abandoned; some partially inactivated vaccines have low efficacy and need to be improved in their protection rates and duration of immunity, such as traditional inactivated influenza and Typhoid vaccine. Most of these ineffective vaccines will be replaced by new vaccines.

Toxoid vaccine

When the pathological changes of the disease are mainly caused by potent exotoxin or enterotoxin, toxoid vaccines have great significance, such as vaccines for tetanus and diphtheria. In general, enterotoxins are rarely successful. However, genetically engineered detoxified variants of the thermostable enterotoxin (LT) of enterotoxigenic E. coli have the potential to become an effective traveler's diarrhea vaccine. Cholera toxin (CT) mutations may become more important vaccines. Variants of these two toxins can even induce good mucosal immunity and are promising mucosal immune adjuvants.

Most currently used toxoid vaccines are manufactured using traditional techniques. These vaccines, such as diphtheria and tetanus vaccine, contain many impurities, and the formaldehyde treatment process that turns toxins into toxoids also results in cross-linking with bovine-derived polypeptides from the culture medium, resulting in unnecessary antigens. Therefore, studying a mutant, non-toxic pure molecule as a new vaccine can improve the quality and efficacy of these vaccines. For example, replacing glutamic acid at position 52 of diphtheria toxin with glycine can cause loss of toxicity and can cross-react with diphtheria toxin.

Subunit vaccines and peptide vaccines

DNA recombination technology makes it possible to obtain a large number of pure antigen molecules. This is a revolutionary change in technology compared to vaccines made with pathogens as raw materials, making quality easier to control and more expensive. From the perspective of effects, some subunit vaccines, such as acellular pertussis and HBsAg, have high immunogenicity at low doses; while other vaccines have lower immunity and require stronger adjuvants than aluminum salts.

Peptide vaccines are usually manufactured by chemical synthesis techniques. Its advantages are simpler ingredients and easier quality control. However, as the molecular weight and structural complexity of the immunogen decrease, the immunogenicity also decreases significantly. Therefore, these vaccines generally require special structural designs, special delivery systems or adjuvants.

Carrier vaccine

Vector vaccines pass antigen genes into the body through harmless microorganisms to induce immune responses. It is characterized by combining the powerful immunogenicity of live attenuated vaccines with the accuracy of subunit vaccines. A significant advantage of this live vector vaccine is that it can effectively induce cellular immunity in vivo, which is very promising in the context of current methods of inducing cellular immunity that are not good enough and cellular immunity is particularly important in some diseases. Important vectors used in the tests were variants of vaccinia virus, poliovirus, fowlpox virus, adenovirus, herpes virus, salmonella, shigella and the like. It is also possible to construct one or more cytokine genes at the same time, which can enhance the immune response or change the direction of the immune response.

Nucleic acid vaccine

Nucleic acid vaccines are also called DNA vaccines or naked DNA vaccines. The key difference from live vaccines is that the DNA encoding the antigen does not replicate in humans or animals. Nucleic acid vaccines should contain a strong promoter element that can be efficiently expressed in mammalian cells, such as the human cytomegalovirus promoter; it should also contain a suitable mRNA transcription termination sequence. After intramuscular injection, DNA enters the cytoplasm and then reaches the nucleus of the muscle cell, but does not integrate into the genome. As target cells of the gene gun method, neither muscle cells nor dendritic cells divide and proliferate at a high speed, nor are they highly homologous to plasmids, so homologous recombination is less likely.

Compared with other types of vaccines, nucleic acid vaccines have potential and huge advantages: DNA vaccine is one of the few methods to induce cytotoxic T cell response; can overcome protein subunit vaccines prone to misfolding and glycosylation The problem of incomplete chemical transformation; Good stability, small possibility of a large number of variations, and easy quality control; Lower production costs. Theoretically, multivalent vaccines can be achieved by a mixture of multiple plasmids or by constructing complex plasmids. Theoretically, the stability of antigen synthesis will reduce the booster injection dose. Very small amounts of DNA (sometimes nanograms) can activate cytotoxic T cells well.

In theory, nucleic acid vaccines also have potential problems or side effects. First, although the possibility of homologous recombination with the host DNA is small, random insertion is still possible. Although there is no quantitative data on this issue, whether to induce cancer is still a concern. Secondly, the DNA vaccine titers are different in different antigens or different species. The effect of human vaccines on model animals should be properly evaluated. Third, the body's immune regulation and effector mechanisms may lead to the destruction of antigen-expressing cells, leading to the release of intracellular antigens and activating autoimmunity. Fourth, the stimulation of small doses of antigens for a long period of time may lead to immune tolerance, resulting in the recipient's non-responsiveness to the antigen. But in practice so far, these potential side effects have not been found.

Edible vaccine

The carrier of such vaccines is to use the cells of edible plants such as potatoes, bananas, and tomatoes to start a protective immune response by eating their fruits or other components. Plant cells as natural biocapsules can effectively deliver antigens to the submucosal lymphatic system. This is one of the few forms currently effective for initiating mucosal immunity. Therefore, it has good development prospects for mucosal infectious diseases. ^[1]

Vaccine contraindications

In China, vaccine taboos are categorized into general taboos and absolute taboos, and foreign books and periodicals call contraindications and caution.

Generally contraindicated refers to the delayed vaccination under certain circumstances, such as fever and disease recovery period (equivalent to a caution card).

Absolute contraindication means that after vaccination, it is possible to increase the probability of occurrence of adverse reactions to the vaccination and increase the adverse reactions or immune damage. Such as immunocompromised (deficient) people, can not be vaccinated with live attenuated vaccine, but can be vaccinated with inactivated vaccine. Those who are allergic to eggs should not be vaccinated against chicken embryo cells such as measles and influenza.

With reference to the 2003 ACIP recommended program, some adults with health conditions can choose to receive certain vaccines. Patients with diabetes, chronic respiratory disease, chronic liver disease (including alcoholic liver), heart disease, can be vaccinated against influenza vaccine, pneumonia polysaccharide vaccine (PCV), hepatitis B vaccine; those with poor renal function can be vaccinated with pneumonia polysaccharide vaccine, type B Hepatitis vaccine; those with immunodeficiency can be vaccinated against pneumonia polysaccharide vaccine and chicken pox vaccine; those infected with HIV can be vaccinated against pneumonia polysaccharide vaccine and chicken pox vaccine. ^[1]

Vaccine coupling

Strictly speaking, vaccination can be divided into three cases: coupling, inducing and exacerbating the original disease.

Coupling means that the recipient is in the incubation period or prodromal stage of a disease at the time of vaccination. Coupling occurs after vaccination. It has no causal relationship with vaccination. It is purely coincidental, that is, the disease will occur regardless of vaccination .

Induction means that the recipient has the vaccination contraindicated in the vaccine instructions, the vaccination before the vaccination or its guardian did not truthfully provide the health status of the vaccination and the vaccination contraindication, etc., after the vaccination, the original disease's acute recurrence or impact Physiological process.

Aggravation means that the recipient originally had a chronic disease, which caused exacerbation or acute recurrence immediately after vaccination. It has been confirmed by investigation that there is a certain relationship with vaccination. Aggravating the original disease is actually a kind of induction, but the clinical symptoms and signs are more serious.

Induction and exacerbation are directly or indirectly related to vaccination, that is, without vaccination, it may not cause recurrence or exacerbation of the original disease.

The "Regulations on the Administration of Vaccine Circulation and Vaccinations" issued by the State Council stipulate that the recipients have the vaccination contraindications prescribed in the vaccine instructions, and that the recipient or his guardian did not truthfully provide the health status and contraindications of the recipient before the vaccination. The acute recurrence or exacerbation of the original disease of the recipient after vaccination does not belong to the prevention of abnormal reactions.

History of vaccine development

The discovery of the vaccine is a landmark event in the history of human development. Because in a sense, the history of human reproduction is the history of human beings' continuous struggle with diseases and natural disasters. The main means of controlling infectious diseases is prevention, and vaccination is considered to be the most effective measure. And it turns out that the same is true. The smallpox virus that has threatened humans for hundreds of years was completely eliminated after the vaccinia vaccine appeared. It ushered in the first victory of humans against the virus with vaccines, and they are even more convinced that vaccines can control and eliminate infectious diseases. Role. After 200 years, the vaccine family has been continuously expanded and developed. There are currently more than 20 vaccines used for the prevention and treatment of human diseases.