Donate

Understanding Vaccine Types: How They Protect Against Disease

The Role of Vaccines in Immunity

How the Immune System Recognizes Pathogens

Our immune system protects us by recognizing, neutralizing, and destroying invading pathogens, which it identifies on the basis of the unique molecules (antigens) they possess. Vaccines harness this process by introducing antigens from a pathogen — such as a virus or bacterium — without causing disease. This exposure trains the immune system to respond effectively. As part of this training, the body creates memory cells that “remember” the antigens, enabling a rapid, targeted response if the pathogen is encountered again, significantly reducing the risk of illness.

Memory Cells and Long-Term Protection

Different types of vaccines deliver these antigens using various methods. Scientists choose the method based on factors like immune response, target population, and available technology. Here’s an overview of the main types and the four broad platforms they fall under.

Inactivated Vaccines

  • How they work: Use dead pathogens to trigger immunity.
  • Key points: May require booster shots for long-term protection.
  • Vaccine examples: Hepatitis A, flu (shot only), polio (shot only), and rabies.

Live-Attenuated Vaccines

  • How they work: Use weakened germs to produce a strong, long-lasting immune response.
  • Key points: Typically provide lifelong protection with 1–2 doses. Not suitable for people with weakened immune systems. Require refrigeration, limiting use in some areas.
  • Vaccine examples: Measles, mumps, rubella (MMR), rotavirus, chickenpox, and yellow fever.

Messenger RNA (mRNA) Vaccines

  • How they work: Use synthetic mRNA to make proteins that trigger an immune response.
  • Key points: Faster to manufacture and carry no risk of causing the disease because they do not contain a live virus. Booster shots may be needed.
  • Vaccine examples: COVID-19, RSV

Subunit, Recombinant, Polysaccharide and Conjugate Vaccines

  • How they work: Use specific parts of the pathogen (such as the essential protein antigen or a carbohydrate) to produce a targeted immune response.
  • Key points: Safe for people with weakened immune systems. Booster shots may be needed.
  • Vaccine examples: Hepatitis B, HPV, whooping cough, pneumococcal disease, meningococcal disease, and shingles.

Toxoid Vaccines

  • How they work: Use an inactivated form of a toxin made by the disease-causing organism to build immunity against its harmful effects. These are sometimes delivered with other chemicals called adjuvants, which increase the immune response
  • Key points: May require booster shots for continued protection.
  • Vaccine examples: Diphtheria and tetanus.

Viral Vector Vaccines

Conjugate Vaccines

  • How they work: Links the pathogen’s sugar molecules to a protein carrier, making it easier for the body to recognize and fight the disease.
  • Key points: Effective against pathogens with sugar-coated surfaces that would otherwise evade detection. Particularly beneficial for young children and individuals with weaker immune responses.
  • Vaccine examples: Hib, pneumococcal disease, and meningococcal disease.