Vaccination

An Overview of the Different Types of Vaccines Available in the World

Vaccines are drugs that are used to immunize humans against certain illnesses. The process of vaccination includes administering the vaccine to counter the disease or illness. They contain the bacteria or viruses that cause sickness and disease or components of the bacteria or viruses that cause illness and disease. The bacteria or virus is put in the vaccine so that the immune system learns to detect it and create antibodies against it if a person is naturally exposed to it without suffering any signs of illness or disease.

Vaccines for Vaccination
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Efficiency of Vaccination

Vaccination can provide active protection to a specific pathogen by boosting the immune system to attack the pathogen. When triggered by a vaccination, the antibody-producing cells, known as B cells (or B lymphocytes), stay sensitized and ready to respond to the agent if it ever enters the body. Vaccination may also provide passive immunity by delivering antibodies or lymphocytes that an animal or human donor has already produced. Medical professionals administer vaccines, usually through injection (parenteral administration). However, some are also taken orally or nasally (in the case of flu vaccine). Vaccines administered to mucosal surfaces, such as those lining the stomach or nasal passages, appear to elicit a more robust antibody response and may be the most effective mode of delivery.

The Very First Vaccines

The first vaccination was developed in 1796 by British physician Edward Jenner, who utilized the cowpox virus (vaccinia) to protect people against smallpox, a similar virus. Before that, however, Asian physicians used the idea of vaccination to protect infants from smallpox by giving them dried crusts from the lesions of patients suffering from the disease. While some people gained immunity, others became infected with the sickness. Jenner’s contribution was to give protection using a material comparable to but safer than smallpox. As a result, he took advantage of the relatively uncommon condition in which immunization to one virus offers protection against another viral illness. In 1881, Louis Pasteur, a French scientist, demonstrated anthrax vaccination by injecting sheep with a mixture containing attenuated strains of the bacillus that causes the illness. Four years later, he acquired a rabies-protective suspension.

Types of Vaccine
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Types of Vaccine

The main types of vaccines that act in different ways are:

  • Live-attenuated vaccines
  • Inactivated vaccines
  • Subunit, recombinant, conjugate, and polysaccharide vaccines
  • Toxoid vaccines
  • mRNA vaccines
  • Viral vector vaccines
  • All vaccinations include the possibility of adverse effects, although some are less likely to do so than others.

Live Attenuated Vaccines

There are various methods for producing attenuated vaccines. First, the disease-causing virus passes via a series of cell cultures or animal embryos in some of the most popular procedures (typically chick embryos). Using chick embryos as an example, the virus is grown in a succession of embryos. With each passage, the virus improves its capacity to reproduce in chick cells while losing its ability to multiply in human cells.

A virus intended for use in a vaccine can be grown—or “passed” through up to 200 separate embryos or cell cultures. The attenuated virus will eventually be unable to multiply correctly (or at all) in human cells and be utilized in vaccines. All approaches involving the passage of a virus via a non-human host result in a virus that can still be detected by the human immune system but cannot reproduce successfully in a human host.

When the resultant vaccine virus is administered to a human, it will not multiply sufficiently to cause sickness. However, it will still elicit an immune response that will protect against future infection.

Live Attenuated Vaccines

One issue to address is the possibility that the vaccination virus will return to a form capable of causing illness. Mutations that might arise during the vaccine virus’s replication in the body may result in a more virulent strain. However, it is pretty rare because the vaccine virus’s capacity to multiply is restricted; yet, it is considered while producing an attenuated vaccination.

It’s worth mentioning that mutations are rather prevalent with the oral polio vaccine (OPV), a live vaccination that’s swallowed rather than injected. As a result, the vaccination virus can evolve into a virulent form, resulting in rare occurrences of paralytic polio. As a result, OPV is no longer used in the United States, and the inactivated polio vaccine has taken its place on the Recommended Childhood Immunization Schedule (IPV).

Vaccination
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Live Attenuated Vaccine Efficiency

  • A live, attenuated vaccination’s protection often outlasts that of a dead or inactivated vaccine.
  • The vaccinations deliver a live version of the germ or virus that causes the disease into the body. Although the germ is alive, it is a weaker variety that does not cause illness symptoms since it cannot multiply once inside the body.
  • Live-attenuated vaccines can be used to develop immunity against viruses or bacteria, although viruses are the most usually utilized.
  • This form of vaccination works by enabling a virus or germ to increase sufficiently for the body to create memory B-cells, which can detect and remember a virus and activate an immune response against it for many years after the initial reaction.
  • Live-attenuated vaccinations induce an immune response comparable to that of a natural infection. Still, the individual cannot spread the virus to others and will not become ill with the disease caused by the virus.
  • The vaccinations give lifetime protection from illness, and only one or two doses of the vaccine are generally required to deliver this immunity.

The types of diseases that live-attenuated vaccines are used for include:

  • Measles, mumps, and rubella (MMR combined vaccine)
  • Rotavirus
  • Smallpox
  • Chickenpox
  • Yellow fever

Because this type of vaccination contains a live form of the virus or bacterium, medical advice is essential before administering the vaccine, as it may not be acceptable for those with compromised immune systems or long-term health concerns.

Live-attenuated should be stored cold. Therefore, they may not be acceptable for use in situations with limited access to refrigeration.

Inactivated

A strain of bacteria or viruses destroyed by heat or chemicals is used in an inactivated vaccination. The body is then injected with a deadly form of the virus or bacterium. Inactivated vaccines are the first form to be developed, and they do not elicit the same robust immune response as live-attenuated vaccinations. Although inactivated vaccinations may not provide lifetime protection and must be replenished over time, they may produce fewer adverse effects than live-attenuated vaccines.

The types of diseases that inactivated vaccines are used for include:

  • Hepatitis A
  • Flu
  • Polio
  • Rabies

Subunit, recombinant, conjugate, and polysaccharide

Specific portions of the germ or virus are used in subunit, recombinant, conjugate, and polysaccharide vaccines. Because they exploit a specific portion of the germ, they can elicit potent immune responses in the host. Although the immune responses are robust, these vaccinations may need to be replenished over time. They are appropriate for those with weaker immune systems and chronic health issues.

These types of vaccines are used to create immunity against the following diseases:

  • Hib (Hemophilus influenza type b)
  • Hepatitis B
  • Human papillomavirus (HPV)
  • Whooping cough
  • Pneumococcal disease
  • Meningococcal disease
  • Shingles
Vaccines
Credit: NIBSC

Subunit and Conjugate

Both subunit and conjugate vaccines contain merely fragments of the viruses against which they protect.

Subunit employ only a portion of a target pathogen to elicit an immune response. It can be accomplished by isolating a single protein from disease and delivering it as a stand-alone antigen. Subunit vaccinations include the acellular pertussis vaccine and the influenza vaccine (in injectable form).

Genetic engineering generates a different form of subunit vaccination. A vaccine protein-coding gene is put into another virus or producer cells in a culture. The vaccine protein is produced when the carrier virus replicates or when the producing cell metabolizes. This method yields a recombinant vaccine: the immune system recognizes the produced protein and provides future protection against the target virus. For example, the current Hepatitis B vaccination used in the United States is a recombinant vaccine.

The human papillomavirus (HPV) vaccination is another genetically engineered vaccine. There are two types of HPV vaccines available—one protects against two strains of HPV and the other against four—but both are generated in the same way: a single viral protein is extracted for each strain. Virus-like particles (VLPs) are formed when these proteins are expressed. These VLPs have no viral genetic material and cannot cause sickness, but they do stimulate an immune response that gives future protection against HPV.

Conjugate Vaccine

Conjugate vaccines are similar to recombinant vaccines in that they are created by combining two distinct components. They, on the other hand, are manufactured from bacterium coat fragments. These coats are chemically attached to a carrier protein, and the resulting combination is utilized to create a vaccine. Conjugate vaccines are used to elicit a more robust, combined immune response: usually, the “piece” of bacteria being introduced would not elicit a significant immune response on its own, but the carrier protein would. As a result, the bacterial fragment cannot cause sickness, but it can develop protection against future infection when associated with a carrier protein. This technology is used to create the pneumococcal bacterial infection vaccines that are now in use for children.

Subunit

Antigens from the germ’s or virus’s surface are responsible for inducing an immune response in the body. Subunit vaccines extract individual antigens from a germ or virus for use in the vaccine. These antigens are carefully selected based on the intensity of the immune response they elicit. Because they are so precisely targeted, subunit vaccinations have few adverse effects.

Recombinant

Genetic engineering is used to create recombinant vaccines. The gene producing the protein for a bacteria/virus is extracted and inserted inside the genes of another cell. When the cell divides, it generates vaccine proteins, indicating that the immune system will identify the protein and defend the body from it.

Conjugate

Conjugate vaccines have two distinct components. First, conjugate vaccines employ elements of the bacteria or virus’s outer antigen coat that are not powerful enough to cause sickness or elicit an immune response in the body.

These weak antigen coatings are chemically connected to a more robust carrier protein. Therefore, combining the weak antigen coat and more muscular carrier proteins causes the immune system to attack the weak antigen aggressively.

Polysaccharide

Polysaccharide vaccines employ sugar molecules (known as polysaccharides) from a bacteria’s or virus’s outer coat. These sugar molecules are chemically bonded to carrier proteins and function similarly as conjugate vaccines do.

Toxoid Vaccine
Credit: Medical News Today

Toxoid

Toxoid vaccines employ toxins produced by bacteria or viruses to generate immunity against particular portions of the bacterium or virus that cause disease rather than the complete bacteria or virus. This particular poison has elicited an immunological response. Toxoid vaccinations do not provide lifetime protection and must be replenished over time. They are used to immunize people against diphtheria and tetanus.

mRNA vaccines

For decades, this technology has been in the works. Short manufacturing timeframes and cheap manufacturing costs are two advantages of mRNA vaccines. However, because of the fragility of the mRNA, they must be stored at low temperatures. mRNA vaccines operate by eliciting an immune response from the proteins they produce. They stimulate cellular as well as humoral immunity. This year, the first mRNA vaccination for COVID-19 was licenced. Some people believe that mRNA vaccinations can change a person’s DNA. However, they are unable to do so.

Viral vector vaccines

Virus vector vaccines alter another infection and use it as a vector to protect against the desired virus. For example, Adenovirus, influenza, measles virus, and vesicular stomatitis virus are employed as vectors (VSV). Recent applications of viral vector technology include the Ebola virus and COVID-19, and research into its application for Zika, flu, and HIV is continuing.

DNA and recombinant vector vaccines

DNA vaccines and recombinant vector vaccines (also known as platform-based vaccinations) are two new forms of vaccines currently being developed. They are made out of DNA that produces particular antigens from germs. The DNA for the germ is generated by the body and detected by the immune system. It is after being injected into the body. The immune response will then protect the body against future infection and will continue to do so.

DNA vaccines are expected to be more successful than protein- or antigen-based vaccinations because antigens can sometimes be damaged or eaten by the body before the immune system can mount a full-fledged attack on the antigen. Recombinant vector types function like a natural infection, educating the immune system to detect and destroy pathogens. They function by replicating a live virus that has been genetically modified to contain additional genes from the germ invading the organism. The additional genes create the proteins that the immune system needs to detect and guard against.

Conclusion

Four types of vaccinations are extensively used against various illnesses, but new vaccines are being researched that may be less expensive and give more extended protection than existing immunizations. The present vaccinations have more significant adverse effects than others, such as the live-attenuated vaccine, which may not be appropriate for persons with long-term health concerns or compromised immune systems. While some vaccines employ live forms of a specific virus or bacteria to elicit an immune response, others can use only a portion of the virus or bacteria to elicit an immune response, which may result in better immunological activity against the germ due to its specificity. Therefore, before getting vaccinated against a specific disease, it is mandatory for everyone to seek medical guidance.

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