Производство вакцин
Традиционные методы производства вакцин основаны на применении ослабленных или убитых возбудителей. В настоящее время многие новые вакцины (например, для профилактики гриппа, гепатита В) получают методами генной инженерии.
A vaccine is a substance that is introduced into the body to stimulate the body’s immune response. It is given to prevent an infectious disease from developing and the person becoming ill.
Vaccines are made from microbes that are dead or inactive so that they are unable to cause the disease. The antigen in the vaccine is the same as the antigen on the surface of the disease-causing microbe. The vaccine stimulates the body to produce antibodies against the antigen in the vaccine. The antibodies created will be the same as those produced if the person was exposed to the pathogen. If the vaccinated person then comes into contact with the disease-causing microbe, the immune system remembers the antibodies it made to the vaccine and can make them faster. The person is said to be immune to the pathogen.
Vaccines are usually given by an injection.
There are four basic types of vaccine in use today
Killed vaccines: These are preparations of the normal (wild type) infectious, pathogenic virus that has been rendered non-pathogenic, usually by chemical treatment such as with formalin that cross-links viral proteins.
Attenuated vaccines: These are live virus particles that grow in the vaccine recipient but do not cause disease because the vaccine virus has been altered (mutated) to a non-pathogenic form; for example, its tropism has been altered so that it no longer grows at a site that can cause disease.
Sub-unit vaccines: These are purified components of the virus, such as a surface antigen.
DNA vaccines: These are usually harmless viruses into which a gene for a (supposedly) protective antigen has been spliced. The protective antigen is then made in the vaccine recipient to elicit an immune response
Live, Attenuated Vaccines
Live, attenuated vaccines contain a version of the living microbe that has been weakened in the lab so it can’t cause disease. Because a live, attenuated vaccine is the closest thing to a natural infection, these vaccines are good “teachers” of the immune system: They elicit strong cellular and antibody responses and often confer lifelong immunity with only one or two doses.
Despite the advantages of live, attenuated vaccines, there are some downsides. It is the nature of living things to change, or mutate, and the organisms used in live, attenuated vaccines are no different. The remote possibility exists that an attenuated microbe in the vaccine could revert to a virulent form and cause disease. Also, not everyone can safely receive live, attenuated vaccines. For their own protection, people who have damaged or weakened immune systems—because they’ve undergone chemotherapy or have HIV, for example—cannot be given live vaccines.
Another limitation is that live, attenuated vaccines usually need to be refrigerated to stay potent. If the vaccine needs to be shipped overseas and stored by healthcare workers in developing countries that lack widespread refrigeration, a live vaccine may not be the best choice.
Live, attenuated vaccines are relatively easy to create for certain viruses. Vaccines against measles, mumps, and chickenpox, for example, are made by this method. Viruses are simple microbes containing a small number of genes, and scientists can therefore more readily control their characteristics. Viruses often are attenuated through a method of growing generations of them in cells in which they do not reproduce very well. This hostile environment takes the fight out of viruses: As they evolve to adapt to the new environment, they become weaker with respect to their natural host, human beings.
Live, attenuated vaccines are more difficult to create for bacteria. Bacteria have thousands of genes and thus are much harder to control. Scientists working on a live vaccine for a bacterium, however, might be able to use recombinant DNA technology to remove several key genes. This approach has been used to create a vaccine against the bacterium that causes cholera, Vibrio cholerae, although the live cholera vaccine has not been licensed in the United States.