Immunology and Vaccines
This section covers immunology and vaccines. The exam tests innate and adaptive immunity, antibody classes, primary and secondary responses, and vaccine types.
Core rules
Innate immunity is fast, non-specific, and has no memory; it includes barriers, phagocytes, complement, and inflammation. Adaptive immunity is specific and has memory, mediated by B cells and T cells. Antibodies are immunoglobulins: IgM appears early in a primary response, IgG dominates later and in secondary responses, IgA is secreted, IgE is linked to allergy, and IgD is a B-cell receptor. Active immunity means the person's own immune system makes antibodies after infection or vaccination. Passive immunity means antibodies are transferred, giving immediate but short-lived protection. Vaccine types include live attenuated, inactivated, subunit, toxoid, and mRNA. Live attenuated vaccines are usually avoided in immunocompromised patients.
Worked example
A child is vaccinated against measles and later exposed to the virus. Memory B and T cells produce a rapid secondary response, usually with high IgG, so disease is prevented or milder. This is active immunity from vaccination. If the child instead receives immunoglobulin after exposure, protection is passive and temporary. The reasoning is the source of antibodies: the child's own immune system versus an external supply.
Traps that cost marks
Do not confuse active and passive immunity. IgM is not the main antibody of a secondary response. Live vaccines are not automatically safe in immunocompromised hosts. Antibiotics are not vaccines and do not create immune memory. Herd immunity protects unvaccinated individuals only when coverage is high.