• A vaccine is a biological preparation that offers active acquired immunity to a specific disease. Generally, a vaccine comprises of an agent that has a resemblance to the disease-causing microbe.
    • Acquired immunity is immunity one develops over a lifetime. It can come from a vaccine, exposure to an infection or disease, or another person’s antibodies (infection-fighting immune cells). 
    • When pathogens (germs) are introduced into the body from a vaccine or a disease, the body’s immune system learns to target those germs in the future by making new antibodies.
  • The agent induces the body’s immune system to recognize the agent as a threat and destroy it. The immune system further memorizes to destroy any of the microorganisms associated with that agent that it may encounter in the future.

How do vaccines work?

  • When viruses or bacteria (germs) invade our body, they attack and multiply. This invasion is called an infection, and the infection is what causes illness.
  • The first time the body encounters a germ, it can take several days for the immune system to make and use all the tools it needs to fight the infection.
  • After the infection has been eradicated, the immune system keeps a few “memory cells” that remember what it learned about how to protect against that disease.
  • If the body encounters the same virus or bacteria again, it will produce antibodies to attack the germ more quickly and efficiently.

Types of vaccines

Vaccines are made up of viruses or bacteria that are altered or weakened so that they only cause an imitation of the disease and not the disease.

There are a variety of different ways to alter or weaken the viruses or bacteria so that vaccination develops immunity instead of serious disease.

Following are the different types of vaccines based on how they are made:

  1. Inactivated Vaccine: Vaccines of this type are created by inactivating a pathogen, 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.
  2. Attenuated Vaccine: Attenuated vaccines can be made in several different ways. Some of the most common methods involve passing the disease-causing virus through a series of cell cultures or animal embryos (typically chick embryos). When the resulting vaccine virus is given to a human, it will be unable to replicate enough to cause illness, but will still provoke an immune response that can protect against future infection.
  3. Toxoid Vaccine: Some bacterial diseases are not directly caused by a bacterium itself, but by a toxin produced by the bacterium. 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.
  4. Subunit Vaccine: Subunit vaccines use only part of a target pathogen to provoke a response from the immune system. This may be done by isolating a specific protein from a pathogen and presenting it as an antigen on its own.
  5. Conjugate Vaccine: Conjugate vaccines are somewhat similar to recombinant vaccines: they’re made using a combination of two different components. Conjugate vaccines, however, are made using pieces from the coats of bacteria. These coats are chemically linked to a carrier protein, and the combination is used as a vaccine
  6. Valence Vaccine: Vaccines may be monovalent. A monovalent vaccine is designed to immunize against a single antigen or single microorganism.A multivalent or polyvalent vaccine is designed to immunize against two or more strains of the same microorganism, or against two or more microorganisms.
  7. Heterotypic Vaccine: Heterologous vaccines also known as “Jennerian vaccines”, are vaccines that are pathogens of other animals that either do not cause disease or cause mild disease in the organism being treated.
  8. mRNA Vaccine: An mRNA vaccine (or RNA vaccine) is a novel type of vaccine which is composed of the nucleic acid RNA, packaged within a vector such as lipid nanoparticles.

mRNA Vaccine

  • The mRNA (messenger RNA) is one such vaccine that injects pieces of mRNA into human cells in order to get them the produce pathogen antigens.
  • The mRNA vaccines function differently from traditional vaccines. Traditional vaccines stimulate an antibody response by injecting a human with antigens. mRNA vaccines inject a fragment of the RNA sequence of a virus directly into the cells, which then stimulate an adaptive immune response mRNA fragment is a specific piece of the virus that carries instructions to build the antigen of the virus. An advantage of RNA vaccines is that they stimulate cellular immunity.
  • Unlike DNA vaccines, mRNA vaccines are more fragile as the molecules degrade within minutes when exposed to the outside environment, hence they need to be stored at extremely low temperatures.
  • Advantages of Using mRNA-Based Vaccines
    • mRNA vaccines are considered safe as mRNA is non-infectious, non-integrating in nature, and degraded by standard cellular mechanisms.
    • They are highly efficacious because of their inherent capability of being translatable into the protein structure inside the cell cytoplasm.
    • Additionally, mRNA vaccines are fully synthetic and do not require a host for growth, e.g., eggs or bacteria. Therefore, they can be quickly manufactured inexpensively to ensure their “availability” and “accessibility” for mass vaccination on a sustainable basis.
mRNA vaccines

How are mRNA Vaccines Different From Traditional Vaccines?

  • Vaccines work by training the body to recognise and respond to the proteins produced by disease-causing organisms, such as a virus or bacteria.
  • Traditional vaccines are made up of small or inactivated doses of the whole disease-causing organism, or the proteins that it produces, which are introduced into the body to provoke the immune system into mounting a response.
  • mRNA vaccines tricks the body into producing some of the viral proteins itself.
    • They work by using mRNA, or messenger RNA, which is the molecule that essentially puts DNA instructions into action. Inside a cell, mRNA is used as a template to build a protein.

Concerns regarding vaccines

  • Vaccines are a special cause of concern, the reason being that some vaccines can cause side effects, as is the case with all medications. The side effects may range from soreness to swelling but are all mild in comparison to the effects of the disease they protect against.
  • But despite the concerns, vaccines are important as they are the best weapons available in the fight against diseases. As disease keeps evolving over time, the vaccines themselves need to keep up.
Conclusion
  • The overwhelming majority of scientists agree that vaccination is a very safe and effective method for preventing infectious diseases and curing those that already exist.
  • The immune system “remembers” vaccination agents because it recognises them as alien, eliminates them, and then “forgets” about them.
  • When the virulent form of an agent is encountered, the body recognises the protein coat that is present on the virus, and as a result, it is ready to respond, first by neutralising the target agent before it can enter cells, and then by recognising and destroying infected cells before that agent can multiply to vast numbers.
  • When the virulent form of an agent is encountered, the body recognises the protein coat that is present on the virus, and as a result, it is prepared to respond.

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