The last few articles introduced the human immune system, and today I would like to introduce you to another topic – vaccines. As I have told you before, the first vaccine was invented in 1796 by Dr. Edward Jenner in England. The first vaccine was invented by Dr. Edward Jenner in England in 1796. Dr. Jenner observed that milkmaids could not catch smallpox, and the pus from cowpox was inoculated into children to make them immune to smallpox. Thus, Dr. sodium made an important contribution to immunology and established the prototype of modern vaccines.
In addition, Louis Pasteur was a major contributor to the development of vaccines. Louis Pasteur was also an important contributor to the development of vaccines. Pasteur proposed preventive vaccination measures and developed the attenuated rabies vaccine in 1885, which was an important milestone in the development of vaccines.
Vaccine classification
In general, vaccines can be roughly divided into two categories according to their functions: therapeutic vaccines and preventive vaccines.
Therapeutic vaccines
Therapeutic vaccines use antibodies to block infection with a disease in patients who are already infected with the disease. This vaccine is mostly used in emergency situations when the patient is infected. After injection, it works against the pathogen in the body. Therefore, this vaccine is a form of “passive immunity“, i.e., it uses the injection of antibodies to defend against foreign pathogens. Another therapeutic vaccine is the “cancer vaccine“, which is used to boost the patient’s immune system to help fight existing cancers, but this topic will be covered in another article.
Prophylactic vaccine
Prophylactic vaccines, as the name implies, use injected antigens to enable human immune cells to recognize and create their own antibodies to fight disease. Prophylactic vaccines have contributed greatly to human medicine, most notably by improving herd immunity and reducing the spread of infectious diseases. Today’s Covid-19 vaccine is one such vaccine. If you would like to learn more about the Covid-19 vaccine, please stay tuned to our website and we will post an article on the Covid-19 vaccine later. After understanding the rough classification, we can then go on to further introduce it.
Prophylactic vaccines can be found underneath the subdivision as:
1. Live-Attenuated
Attenuated living virus vaccine is made by cultivating the pathogens after attenuating them, in order to reduce the activity of the pathogens, and can be further divided into attenuated living virus vaccine. Although it sounds complicated, the main point of a live virus vaccine is that it is a vaccine made from a live pathogen. Common live vaccines include BCG (Bacillus Camette-Guerin), Sabin vaccine for polio, Measles, Mumps and Rubella (MMR), Varicella vaccine, etc.
Here we would like to remind you that there is another vaccine for poliomyelitis called Salk vaccine, but Salk vaccine is a non-activated virus vaccine and the Sabin vaccine is made differently.
2. Inactived
Inactived vaccines include dead bacterial vaccines and inactivated virus vaccines. In short, a inactived vaccine is a vaccine made by killing a pathogen with heat or chemical agents (Ex: formaldehyde, ethanol). The human body is immunized by recognizing specific proteins or antigenic fragments on the pathogen. Common deadly vaccines include: Cholera vaccine, Typhoid vaccine, Yersinia pestis vaccine, etc. Common inactivated viruses include: Japanese Encephalitis vaccine, Rabies vaccine, Influenza vaccine, etc.
3. Toxoid vaccine
Toxoid vaccines are vaccines that use toxins produced during the culture of pathogens and are treated with chemical agents to make them less toxic but still antigenic. Including tetanus toxoid vaccine, diphtheria toxoid vaccine.
Items 4-7 below are vaccines synthesized using genetic recombination techniques:
4. Conjugated vaccines
Conjugate vaccines use the polysaccharide structure on the surface of the pathogen for structural modification, i.e., adding other functional groups, such as proteins or toxins, to the polysaccharide to improve the immune system’s ability to recognize it. This type of genetic recombination has been successfully used in Haemophilus influenza type b (Hib) vaccines.
5. Recombinant carrier vaccines
A recombinant vector vaccine is based on a microbial vector into which a target gene is transferred and then delivered to a human for immunization. The vector is transcribed and translated in the human body to create the relevant antigen, which is then recognized by the body’s immune cells to produce immunity. Common carriers are adenovirus carriers. AstraZeneca’s COVID-19 vaccine is produced in this manner.
6. Nucleic acid vaccine
Nucleic acid vaccines can be divided into two platforms, DNA and RNA, by injecting the DNA or RNA of the virus directly into the body to produce the relative proteins that stimulate the body to produce antibodies. DNA vaccines are more stable than RNA vaccines, however, the main challenge is to achieve efficient antigen expression. Nucleic acid vaccines are the ideal vaccine platform, with advantages including ease of design and production for rapid and large scale production, while Moderna COVID-19 vaccine is an mRNA vaccine in this category.
7. Subunit antigen vaccine
A subunit antigen vaccine is a vaccine that uses some component of the pathogen instead of the whole pathogen, commonly a protein. The MVC covid-19 vaccine, the Novavax vaccine, uses this technique to create a spike protein on the surface of the virus, which is then delivered to the human body for the immune system to respond. The advantage of this approach is that it is safer, but the disadvantage is that it is less immunogenic and requires adjuvants to increase antigenic immunity.
Finally, we will put up a comparison table for your reference.
Conclusion
Thanks to the development of vaccines, many infectious diseases have been eradicated. Of course, this is also due to the strong immune system of human beings. However, we need to be aware of the potential risks behind vaccines, both in terms of their side effects and their genetic effects, which can be significant. It is expected that medical advances will make future vaccines more effective and safer to enhance human well-being. For those who want to learn more about the human immune system, please read the following article:
References:
- Types of vaccine 🔗
- History of vaccine 🔗
- Francis MJ. Recent Advances in Vaccine Technologies. Vet Clin North Am Small Anim Pract. 2018;48(2):231-241. doi:10.1016/j.cvsm.2017.10.002 🔗
- Cover Image from Pixabay 🔗
