A vaccine is a biological preparation that provides active acquired immunity to a particular infectious disease. It typically contains an agent that resembles a disease-causing microorganism and is often made from weakened or killed forms of the microbe, its toxins, or one of its surface proteins. The vaccine stimulates the body's immune system to recognize the agent as a threat, destroy it, and keep a record of it, so the immune system can more easily recognize and destroy any of these microorganisms that it later encounters.
The vaccine contains antigens, which are parts of the pathogen (such as proteins or sugars) that trigger an immune response. These antigens are harmless on their own and cannot cause disease.
When the vaccine is administered, the immune system detects the antigens and responds by producing immune cells, including T-cells (which help destroy infected cells) and B-cells (which produce antibodies).
The B-cells produce antibodies specific to the antigens introduced by the vaccine. These antibodies can bind to the pathogen if the body encounters it in the future, neutralizing the threat.
After the initial immune response, the body creates memory T-cells and B-cells that remain in the body for a long time, often years or even a lifetime. These memory cells "remember" the pathogen, allowing the immune system to respond more quickly and effectively if it encounters the pathogen again.
If the vaccinated person is later exposed to the actual pathogen, their immune system is primed to respond rapidly, producing antibodies and mobilizing immune cells to fight off the infection before it can cause serious illness.
Contain a weakened form of the live virus or bacteria that can still replicate but cannot cause serious disease in healthy individuals.
Examples: Measles, Mumps, Rubella (MMR) vaccine; Varicella (chickenpox) vaccine.
Contain a virus or bacteria that has been killed or inactivated, so it cannot replicate but still triggers an immune response.
Examples: Polio vaccine, Hepatitis A vaccine.
Contain only specific parts of the virus or bacteria (like proteins or sugars) that best stimulate the immune response.
Examples: HPV vaccine, Hepatitis B vaccine.
Contain inactivated toxins (toxoids) produced by the bacteria that cause the disease. These vaccines create immunity to the parts of the germ that cause a disease rather than the germ itself.
Examples: Diphtheria and Tetanus vaccines.
Contain messenger RNA (mRNA) that encodes a viral protein. When introduced into the body, cells use the mRNA to produce the viral protein, which then triggers an immune response.
Examples: COVID-19 vaccines (Pfizer-BioNTech, Moderna).
Use a different virus as a vector to deliver genetic material from the pathogen, causing cells to produce the pathogen protein and trigger an immune response.
Examples: COVID-19 vaccines (AstraZeneca, Johnson & Johnson).
Vaccines are a critical tool in preventing infectious diseases. By introducing a harmless form of the pathogen to the immune system, vaccines prepare the body to fight off future infections, providing long-term immunity and contributing to public health by reducing the spread of diseases.
