Overview
- 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 into two basic types:
live-attenuated (bacterial or viral) vaccines and
inactivated or non-live vaccines. - Examples of live-attenuated vaccines include measles, mumps, rubella, varicella, yellow fever, oral polio (OPV), rotavirus, live-attenuated influenza (LAIV, “nasal spray”), and BCG.
- Attenuation results in microorganisms that may still infect and multiply in humans, but do not cause disease. Some live vaccines can induce lifelong immunity.
- Inactivated or non-live vaccines include those against hepatitis A, influenza, pertussis, rabies, and polysaccharide vaccines targeting encapsulated bacteria (Haemophilus influenzae type b, Streptococcus pneumoniae, Neisseria meningitidis).
- Most non-live vaccines generally require additional doses (“boosters”) to maintain long-term protective immunity.
- There are additional subcategories of these groups, such as subunit vaccines, whole cell vaccines, toxoid vaccines, polysaccharide vaccines, recombinant protein vaccines, mucosal vaccines, DNA, mRNA vaccines, and vector vaccines.
