Vaccinations are one of the most important methods of disease prevention and play an integral role in public health. But have you ever wondered how they work? What effects do they have on the human body? Why are they so important?

In order to answer these questions, we first need to understand some basics about how the immune system works. The purpose of the immune system is to recognize bacteria and viruses (collectively referred to as pathogens) that can make you sick and to fight off infections. Pathogens have molecules, called antigens, that the immune system identifies as threatening. Once these antigens are spotted, a healthy immune system produces two illness-fighting weapons: a protein called an antibody and a special type of white blood cell called a lymphocyte. Together, antibodies and lymphocytes destroy antigens so that the body can to return to its normal state of health.1

Vaccinations enable the immune system to recognize bacteria and viruses before they have a chance to make you sick. Vaccines introduce the immune system to a previously unknown germ by giving the body a pathogen that is weakened, dead, modified, or genetically engineered. Then, if a body happens to be exposed to that same pathogen a second time, the immune system recognizes it and is already equipped to produce antibodies and lymphocytes that prevent an illness from taking hold.2

While there are some bacteria and viruses your immune system can destroy without vaccinations, others are so powerful that without the help of vaccinations, the immune system is not able to recognize and respond to these threats fast enough. Contagious diseases such as measles, rabies, and smallpox can cause significant health risks, even death, after the very first time a body is exposed to the pathogen, unless that initial exposure is through a controlled exposure through vaccination.

The first vaccine was created in 1796 by British physician Edward Jenner. He injected material from a cowpox virus into patients in order to prevent them from getting smallpox.3 Since the late 18th century, the development of vaccines has revolutionized the field of public health and prevented the spread of a variety of diseases. A brief timeline of vaccine development includes:4

  • Rabies – 1885
  • Cholera – 1896
  • Typhoid – 1896
  • Plague – 1897
  • Pertussis (whooping cough) – 1926
  • Tetanus – 1926
  • Tuberculosis – 1927
  • Influenza (flu) – 1936
  • Polio – 1955
  • Measles – 1963
  • Varicella (chickenpox) – 1995
  • HPV (human papillomavirus) – 2006
  • Zoster (shingles) – 2006
  • COVID-19 – 2020

Historically, the two types of vaccines that have been most commonly used are whole pathogen vaccines and subunit vaccines:

  • Whole pathogen vaccines: These vaccines use an entire virus that has been either killed (inactive) or very weakened viruses (attenuated). Examples of whole pathogen vaccines include the flu shot (inactive) and measles, mumps, rubella (MMR) vaccine (attenuated).
  • Subunit vaccines: Rather than using the entire virus (like whole pathogen vaccines), manufacturers of subunit vaccines use a small signature protein subunit of the virus (antigen). Examples of subunit vaccines include: Hepatitis B, pneumonia, and shingles vaccines.

The next generation in vaccine development is represented in mRNA vaccines (nucleic acid vaccines). What makes mRNA vaccines different?

  • In mRNA vaccines, a vaccinated person receives genetic material, mRNA, that encodes for a specific viral protein. When the mRNA is injected into the arm, cells in the injected person start producing antigen subunits. These antigen subunits provide the immune system with a preview of what the real virus looks like without causing the disease. The body responds to the preview of the antigen by creating both antibodies and memory B cells. The antibodies and memory B cells stay in the body so that if the person has an exposure to the virus, the body is prepared and can destroy the virus so that the person does not become infected.

After a vaccine is administered, patients may experience mild side effects such as soreness or pain in the area of the injection or low-grade fever.5 However, it is important to note that the benefits of vaccines far outweigh the risks. When vaccines are refused, the risk of developing a vaccine-preventable disease increases not only in the individual but also within communities. A certain level of immunity—when the body is able to resist a disease—in the overall population is necessary to prevent sustained person-to-person transmission of a contagious disease.6 Widely publicized outbreaks of diseases like measles, polio, and pertussis are a few examples of how vaccine-preventable diseases can cause significant illness and public health crises.

Some have expressed concern regarding a connection between vaccines and autism. Scientific studies have shown no link between vaccines and autism.7In addition, some parents have expressed concern regarding their children receiving multiple vaccinations during one pediatric visit. Scientific data does not reveal any adverse outcomes with children receiving multiple vaccinations during one clinic visit. The Advisory Community on Immunization Practices and American Academy of Pediatrics recommend that all children receive their vaccinations at their scheduled clinic visits and to follow their immunization schedule.8

Immunity can be achieved when vaccinations are given according to the recommended immunization schedule. Your healthcare provider can help you ensure that you are up to date with all the recommended vaccinations.

This article is not intended to diagnose or treat any condition or to give medical advice. Always consult your primary care provider for healthcare instructions. External links are provided as references and do not indicate an endorsement by Medcor. External links are subject to other sites’ terms of use and privacy policies.

[1] World Health Organization, “How the Immune System Works,”

[2] World Health Organization, “How Vaccines Work,”

[3] World Health Organization, “History of Vaccine Development,”

[4] Stanley Plotkin, “History of Vaccination,” PNAS 111, no. 34 (2014), doi: 10.1073/pnas.1400472111

[5] Centers for Disease Control and Prevention, “Common Questions About Vaccines,”

[6] Julie A. Boom and C. Mary Healy, “Standard childhood vaccines: Parental hesitancy or refusal,” UptoDate, updated November 6, 2019.

[7] Ibid.

[8] Centers for Disease Control and Prevention, “Multiple Vaccines and the Immune System,”