Passive immunity

Passive immunity is protection against infection supplied by antibodies made elsewhere and transferred to a recipient. It acts immediately but usually fades as the antibodies are cleared.

Antibody: An antibody is a protein that binds a specific molecular target, such as part of a pathogen. Passive immunity works by supplying antibodies that bind pathogens or their toxins.
Rabies immunoglobulin: Rabies immunoglobulin is a preparation of antibodies given after a possible rabies exposure. It provides immediate antibodies at the wound while rabies vaccination builds the recipient’s own response.
Active immunity: Active immunity is protection generated by a person's own immune response after infection or vaccination. Unlike passive immunity, it can produce immune memory and longer-lasting protection.
Post-exposure prophylaxis: Post-exposure prophylaxis is treatment given after a suspected exposure to prevent infection or disease. Passive antibodies can be part of urgent prophylaxis when protection is needed before an active response develops.
Antibody-dependent enhancement: Antibody-dependent enhancement is an increase in pathogen entry or disease severity mediated by antibodies under particular conditions. It is a safety concern assessed for some antibody-based interventions, though it is not a general effect of passive immunity.
Placental transfer of IgG: Placental transfer of IgG is the movement of maternal immunoglobulin G across the placenta to the fetus. This route supplies fetal antibodies before birth and protects newborns for a limited time.
Tetanus immune globulin: Tetanus immune globulin is a human antibody preparation used to neutralize circulating tetanus toxin. It supplies antitoxin when exposure or disease requires protection faster than vaccination can provide.
Vaccination: Vaccination exposes the immune system to an antigen or its instructions to build protective immunity. Vaccines generally stimulate active immunity rather than transferring ready-made antibodies.
Serum sickness: Serum sickness is an immune-complex reaction that can follow exposure to foreign proteins, including some antibody products. Some animal-derived passive antibody treatments can trigger this delayed adverse reaction.
Antimicrobial resistance: Antimicrobial resistance is the ability of microbes to survive treatments that would otherwise inhibit or kill them. Pathogens can evolve changes that reduce the effectiveness of therapeutic antibodies.

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