Vaccines and Immunization
- Imagine a world without vaccines.
- Diseases like smallpox, polio, and measles would still be rampant, causing widespread suffering and death.
- Vaccines have transformed global health, but how do they work?
- Think of a vaccine as a training session for your immune system.
- It prepares your body to fight a pathogen without exposing you to the full-blown disease.
What Is a Vaccine?
Vaccine
Vaccines are biological preparations that contain antigens or nucleic acids (DNA or RNA) from a pathogen.
- A vaccine is a biological preparation designed to stimulate the immune system to recognize and fight specific pathogens.
- It does this by introducing antigens or genetic material (DNA or RNA) that codes for antigens.
Types of Vaccines
- Live Attenuated Vaccines
- Contain a weakened form of the pathogen.
- Stimulate a strong immune response.
- Examples: Measles, mumps, and rubella (MMR) vaccine.
- Inactivated Vaccines
- Contain a killed form of the pathogen.
- Safer for people with weakened immune systems.
- Examples: Polio and influenza vaccines.
- Subunit Vaccines
- Contain specific antigens (usually proteins) from the pathogen.
- Focus the immune response on key targets.
- Examples: Hepatitis B and HPV vaccines.
- Nucleic Acid Vaccines (DNA or RNA)
- Contain genetic instructions for making an antigen.
- Human cells produce the antigen, triggering an immune response.
- Examples: COVID-19 vaccines like Pfizer/BioNTech (mRNA).
- Vaccines do not cause the disease they protect against.
- They mimic infection to train the immune system.
How Vaccines Work
1. Introducing the Antigen
Vaccines introduce antigens or genetic material coding for antigens into the body.
2. Activating the Immune System
- Recognition: Antigens are detected by helper T-lymphocytes.
- Activation: Helper T-cells activate B-lymphocytes, which produce antibodies specific to the antigen.
- Response: Antibodies neutralize the antigen, and phagocytes engulf and destroy it.
- The Pfizer/BioNTech COVID-19 vaccine uses mRNA to instruct cells to produce the spike protein of the virus.
- This spike protein acts as an antigen, triggering an immune response.
3. Creating Memory Cells
- Vaccines stimulate the production of memory B-cells and memory T-cells.
- These cells "remember" the antigen, enabling a rapid and strong response if the pathogen is encountered again.
This is why vaccinated individuals often experience milder symptoms or no symptoms at all if exposed to the actual pathogen.
The Importance of Vaccines
Vaccines are essential for preventing diseases and controlling the spread of infections. Here’s why vaccines are so crucial:
1. Disease Prevention
- Vaccines prevent diseases by stimulating the immune system without causing the illness.
- Vaccination reduces the number of people who can get sick and, in turn, reduces transmission within the community.
2. Activation of Herd Immunity
- Herd Immunity is when a large portion of a population becomes immune to a disease, either through vaccination or prior infection.
- When enough people are immune, the disease cannot spread easily because there are fewer people to infect.
3. Eradication of Diseases
- Vaccination programs have been crucial in the eradication or significant reduction of deadly diseases like smallpox and polio.
- Ongoing vaccination efforts aim to eliminate diseases like measles and rubella.
For measles, about 93% of the population needs to be vaccinated to achieve herd immunity.
COVID-19 Vaccination Efforts
- The COVID-19 vaccine rollout has been crucial in controlling the pandemic. Vaccines have drastically reduced severe cases and hospitalizations.
- Widespread vaccination has also contributed to reducing transmission of the virus and improving herd immunity.
- How do ethical considerations influence vaccine distribution in low-income countries?
- Should wealthier nations prioritize sharing vaccines globally?
- What is the purpose of a vaccine?
- How do vaccines activate immunity without causing disease?


