• Vaccines are biological preparations, often made from attenuated or killed forms of microorganisms or fractions thereof.
  • They work by stimulating the immune system to produce antibodies and cells directed against a particular organism, mimicking "natural infection".
  • Based on their biological and chemical characteristics, vaccines can be categorized in two basic types, "Live-attenuated" (bacterial or viral) vaccines and "inactivated" or "non-live" vaccines.
  • Examples of live attenuated vaccines include: Measles, Mumps and Rubella, Varicella, Yellow fever, Oral polio (OPV), rotavirus, the "nasal-spray" Live Attenuated Influenza (LAIV) vaccine and BCG.
    • Attenuation results in micro-organisms that may still infect and multiply in humans, but they usually do not cause severe disease. These vaccines are usually associated to life-long immunity.
  • Inactivated or non-live vaccines include those against hepatitis A, influenza-virus, Bordetella pertussis, rabies-virus or polysaccharide vaccines directed against encapsulated bacteria (Haemophilus influenzae type b, Streptococcus pneumoniae, Neisseria meningitidis A, C W, Y (not group B)).
    • Most non-live vaccines induce a less robust immune response compared to live vaccines. They generally require additional doses ("boosters") to maintain long-term protective immunity.
  • There are many other subcategories of these basic groups, like subunit vaccines, whole cell vaccines, toxoid vaccines, polysaccharide vaccines, recombinant protein vaccines, mucosal vaccines, mRNA or DNA and vector vaccines.