Vaccines and Vaccination

Vaccination puts the immune system's memory (section 7.3) to work before a person is ever exposed to a real, disease-causing pathogen. A vaccine is a preparation made from antigenic material derived from a pathogen — this may be the whole pathogen in a weakened (attenuated) or killed (inactivated) form, isolated proteins from its surface (a subunit vaccine), or its inactivated toxin (a toxoid). When introduced into the body, the vaccine's antigens are harmless enough not to cause the actual disease, but they are still recognised by the immune system as foreign.

The immune system responds to the vaccine exactly as it would to a real infection: it produces antibodies against the vaccine's antigens and, critically, it also generates long-lived memory B- and T-cells. If the real pathogen is encountered later, these memory cells are already primed and ready, and the resulting secondary immune response is fast and powerful enough to destroy the pathogen before it can multiply and cause noticeable illness.

India runs a large Universal Immunisation Programme that protects infants and children against several serious diseases through vaccines such as BCG (for tuberculosis), the oral polio vaccine (OPV), the DPT vaccine (against diphtheria, pertussis, and tetanus), and the MMR vaccine (against measles, mumps, and rubella). More recently, during the COVID-19 pandemic, vaccines developed specifically against SARS-CoV-2 (see section 7.10), such as Covishield and Covaxin, were administered on a massive scale across India and significantly reduced severe illness and death from the disease. …