What You Should Know About Vaccines

What are Vaccines?

The Centre of Disease Control and Prevention (CDC) defines vaccines as a product that stimulates the immune system to produce immunity to a specific disease.

Vaccines most often are comprised of a weakened version of a distinct pathogen. This is done in a way that renders the pathogens incapable of inducing infection, while still being intact for our immune system to recognize them as foreign. Vaccines allow our body to produce specific antibodies and immunological memory against future infection.

How do Vaccines Work?

To learn how vaccines work, we should first understand how our immune system works.

Your immune system is composed of organs, cells, and tissues. Normally when a cell is infected with a pathogen (virus or bacteria), key cells of your immune system, lymphocytes, also known as T and B cells are activated. The T and B cells produce antibodies and cytotoxic T cells that directly destroy the pathogens. Memory T cells are also produced so if the body is re-exposed to the same pathogen, the immune response will be quicker and more effective.

Certain molecules from the pathogens (antigen) are taken and using DNA technology the antigens are weakened so they reproduce very poorly in our body. Virus often cause disease when they reproduce themselves in our body. Natural viruses reproduce 1000 times while antigens in vaccines reproduce around 20 times, not enough to cause disease but enough to induce memory B and T cells. These memory cells learn to recognize pathogens as invaders and then produce antibodies which will recognize antigens immediately and attach aggressively before the pathogens can spread cause illness. The immunity that is provided by the weakened pathogen is not temporary, but rather life-long.

Herd Immunity

The direct benefits of vaccinations means direct protection to individuals that are vaccinated. However, vaccination comes with indirect benefits. The indirect benefits are associated with protective effects observed in unvaccinated populations. This is known as herd effect or herd immunity. Public Health officials state that if 70% of the population is vaccinated then diseases could be entirely eliminated.

Types of Vaccines

There are four main types of vaccines.

1. Live-attenuated vaccines
   • Use a weakened form of the pathogen that causes a disease. These vaccines create a strong and long-lasting immune response where just one or two doses can give you a life-time protection against the disease.  Live vaccines are used to protect against:
     • Measles, Mumps, Rubella (MMR combined vaccine)
     • Rotavirus
     • Smallpox
     • Chickenpox
     • Yellow fever
2. Inactivated vaccines
   • Use the killed form of the pathogen that causes a disease. These vaccines do not provide immunity thus you need several booster shots in order to get ongoing immunity.
     • Hepatitis A
     • Flu shots
     • Polio
     • Rabies
3. Subunit, recombinant, polysaccharide and conjugate vaccines
4. Toxoid vaccines

Main Ingredients in Vaccine

Sources

R. S. Federman. Understanding Vaccines: A Public Imperative. Yale J Biol Med. 87, 417-422 (2014).  

T. H. Kim, J. Johnstone, M. Loeb. Vaccine Herd Effect. Scand. J Infect. Dis. 43, 683-689 (2011).  

CDC. (2015, October 27) Vaccines Do Not Cause Autism Concerns. Centers for Disease Control and Prevention. Center for Disease Control and Prevention.

S. Sampson. (2018, December 6) Everything You Need to Know About Vaccinations. Healthline. Retrieved from https://www.healthline.com/health/vaccinations. 

Anon. (2017, December) Vaccine Types. HHS.gov . Retrieved from https://www.vaccines.gov/basics/types.

A. S. Clam. Fundamentals of Vaccine Immunology. J. Glob. Infect Dis. 3, 73-78 (2011).