A look into the four different types of vaccines
Written by Shriya
In the previous article of this series, we took a look at the history of vaccines, including a timeline of their advancements and key scientific figures. As time has progressed, vaccines have further developed and become more effective. They have been studied on a deeper level, which has allowed them to be classified and better understood.
Vaccines teach the body to defend itself when germs, such as viruses or bacteria, invade it. They do so by exposing a person to a very small, safe amount of these viruses or bacteria. Since they have been weakened or killed, the germs do not pose a threat to a person’s health. Rather, the immune system learns to recognize and attack the infection if a person is exposed to it later in life. As a result, they will not become ill or have a milder infection if they do. In this way, vaccines are a natural way to deal with infectious diseases.
While they all serve the same general purpose to protect peoples’ health, there are different types of vaccines that are classified based on how they are made. In this article, we will learn more about the four different vaccines:
Live-attenuated vaccines
Inactivated vaccines
Subunit, recombinant, polysaccharide, conjugate vaccines
Toxoid vaccines
Live-Attenuated Vaccines:
Live attenuated vaccines are produced by modifying a disease-producing (“wild”) virus or bacterium in a laboratory. The resulting vaccine organism retains the ability to replicate (grow) and produce immunity, but usually does not cause illness. (1) To produce an immune response, live attenuated vaccines must replicate in the person. After a small dose of the virus or bacteria is administered, it can replicate in the body and produce an immune response. It may seem as if replicating the virus can cause a disease. However, this usually does not occur and when it does, the adverse reaction is usually milder than the natural disease would be. The immune response to a live attenuated vaccine is virtually identical to that produced by a natural infection. The immune system does not differentiate between an infection with a weakened vaccine virus and an infection with a wild virus.
Since these vaccines are so similar to the natural infection that they help prevent, they create a strong and long-lasting immune response. Just 1 or 2 doses of most live vaccines can give a lifetime of protection against a germ and the disease it causes. (2) Live attenuated vaccines are fragile and can be damaged or destroyed by heat and light. Therefore, they must be handled and stored carefully, which can restrict their ability to be transported. Active immunity from a live attenuated vaccine may not develop because of interference from circulating antibodies to the vaccine virus. In rare cases, live attenuated vaccines can lead to severe or fatal reactions by causing uncontrolled replication of the virus. This only occurs in persons with immunodeficiency (e.g., from leukemia, treatment with certain drugs, or human immunodeficiency virus [HIV] infection). (1)
Creates immunity against:
Measles
Mumps
Rubella
Vaccinia
Varicella
Yellow Fever
Rotavirus
Influenza
Inactivated Vaccines
Inactivated vaccines are produced by first growing the bacterium or virus in culture media. Then the pathogen is inactivated, typically using heat or chemicals such as formaldehyde or formalin. This destroys the pathogen’s ability to replicate, but keeps it “intact” so that the immune system can still recognize it. (3)
Inactivated vaccines do not contain live viruses or bacteria and cannot replicate. Therefore, these vaccines cannot cause disease from infection, even in people who are suffering from immunodeficiencies. This provides a benefit over live-attenuated vaccines, especially for those who have a more vulnerable immune system. In contrast to live vaccines, in which the immune response closely resembles natural infection, the immune response to an inactivated vaccine is small in that little or no cellular immunity results. Therefore, the first dose of an inactivated vaccine does not produce protective immunity, but instead “primes” the immune system. A protective immune response develops after the second or third dose. (1) Additionally, antibody titers against inactivated antigens do diminish with time. As a result, some inactivated vaccines may require periodic supplemental doses to increase, or “boost,” antibody titers. These are known as booster shots.
Creates immunity against:
Hepatitis A
Polio
Rabies
Influenza
Subunit, Recombinant, Polysaccharide, and Conjugate Vaccines
Subunit, recombinant, polysaccharide, and conjugate vaccines use specific pieces of the germ, such as its protein, sugar, or capsid (a casing around the germ). Since these vaccines use only specific pieces of the germ, they can provide a strong immune response that is targeted to the key parts of the germ.
Subunit vaccines
Antigens from the surface of the germ or virus are responsible for triggering an
immune response in the body. Subunit vaccines isolate specific antigens from a
germ or virus for use in the vaccine, and these antigens are specifically chosen
according to the strength of the immune response they generate. (4)
Recombinant vaccines
Recombinant vaccines are made through genetic engineering. The gene that
creates the protein for a bacteria or virus is isolated and placed inside another
cell’s genes. When that cell reproduces, it produces vaccine proteins that mean
the immune system will recognize the protein and protect the body against it.
Conjugate vaccines
Conjugate vaccines use two different components. They use parts from the outer
antigen coat of the bacteria or virus, which are not strong enough to cause illness
or generate an immune response in the body. These weak antigen coats are
linked to a stronger carrier protein using chemicals, and this combination of the
weak antigen coat and stronger carrier proteins trigger the immune system to act
more aggressively against the weak antigen. In this way, the combined piece of bacteria
and the carrier protein can generate immunity against future infection. (4)
Polysaccharide vaccines
Polysaccharide vaccines use sugar molecules (known as polysaccharides) from the
capsule (outer layer) of a bacteria or virus. These sugar molecules are chemically linked
to carrier proteins and work similarly to conjugate vaccines. This type of vaccine can
generate a protective immune response in older children and adults and cannot cause the
disease. (4) Repeated doses of most inactivated protein vaccines cause the antibody titer
to go progressively higher, or “boost.” This does not occur with polysaccharide antigens;
repeat doses of polysaccharide vaccines usually do not cause a booster response.
Antibody induced with polysaccharide vaccines has less functional activity than that
induced by protein antigens.
Subunit, recombinant, polysaccharide, and conjugate vaccines can be used on most people, including those with a weakened immune system and long-term health problems. This is because the vaccines are so specifically targeted, and therefore do not cause many side effects. Although the immune responses are strong, these types of vaccines may need topping up over time. One limitation of these vaccines is that you may need booster shots to get ongoing protection against diseases.
Creates immunity against:
Hib (Hemophilus influenza type b)
Hepatitis B
Human papillomavirus (HPV)
Pneumococcal disease
Meningococcal disease
Shingles.
Toxoid Vaccines
Toxoid vaccines use a toxin (harmful product) made by the germ that causes a disease. Immunizations for this type of pathogen can be made by inactivating the toxin that causes disease symptoms. As with organisms or viruses used in killed or inactivated vaccines, this can be done via treatment with a chemical such as formalin, or by using heat or other methods. (3) They create immunity to the parts of the germ that cause a disease instead of the germ itself. That means the immune response is targeted to the toxin instead of the whole germ.
Similarly to the other types of vaccines, toxoid vaccines can require booster shots to provide an ongoing protection against diseases.
Creates immunity against:
As vaccine developments continue, new types of vaccines are being discovered. DNA and Recombinant Vector vaccines are two new types of vaccines currently under development.
DNA vaccines include DNA that creates specific antigens from a germ. Once injected into the body, the DNA for the germ is reproduced by the body and is recognized by the immune system. (4) Then, the immune response will protect the body against further infection and continue to provide protection in the future. DNA vaccines are thought to be more effective than protein or antigen based vaccines since there is not an antigen that can be degraded or consumed by the body before the immune system can generate a full attack against the antigen.
Recombinant vector vaccines work as a natural infection and are good at training the immune system to recognize and attack germs. They work by reproducing a live virus that has been engineered to carry extra genes from the germ infecting the body. The extra number of genes produce the proteins that the immune system needs to recognize and protect against. (4)
The different types of vaccines all pose benefits and limitations. Therefore, which type of vaccine to use depends purely on the person and the disease in question. Through further progress, vaccines can be improved to reduce adverse symptoms and promote effectiveness. The future of vaccines is promising and will only continue to advance.
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