# Passive Immunisation and Immunoglobulin Products

> Passive immunisation for NEET-PG Microbiology: hyperimmune globulins, equine antisera, rabies and tetanus prophylaxis, serum sickness and product timing.

- Canonical URL: https://prepelephant.com/topics/neet-pg/microbiology/passive-immunisation-and-immunoglobulin-products
- Exam / course: NEET-PG · Subject: Microbiology
- Publisher: PrepElephant (https://prepelephant.com) — Prepared and reviewed by the PrepElephant Academic Review Team
- First published: 2026-10-14
- Last updated: 2026-10-14
- Reference basis: Ananthanarayan and Paniker's Textbook of Microbiology; Murray's Medical Microbiology; IAP Guidebook on Immunization
- How to cite: "Passive Immunisation and Immunoglobulin Products", PrepElephant, https://prepelephant.com/topics/neet-pg/microbiology/passive-immunisation-and-immunoglobulin-products

## Direct answer

Passive immunisation gives a person ready-made antibody, so protection is immediate but temporary, and no immunological memory is created. Immunoglobulin products come from pooled human plasma, from hyperimmune donors or from immunised animals as antisera. Hyperimmune globulins such as rabies and tetanus immunoglobulin are given after exposure, when vaccine alone would act too slowly to prevent disease.

## What you must remember

- **Passive immunity:** antibody transferred from another source, giving protection within hours that wanes over weeks, with no memory response.
- **Active versus passive:** vaccination gives lasting protection with memory, while immunoglobulin covers the gap until the body responds.
- **Human normal immunoglobulin:** pooled plasma from many donors, used for antibody deficiency and for some post-exposure prophylaxis.
- **Hyperimmune globulins:** plasma from donors with high antibody titres, such as hepatitis B immunoglobulin, rabies immunoglobulin and tetanus immunoglobulin.
- **Tetanus immunoglobulin:** human tetanus immunoglobulin, 250 IU intramuscularly, is given with toxoid after a tetanus-prone wound when vaccination history is uncertain.
- **Antisera:** serum from immunised horses, such as diphtheria antitoxin, is effective but heterologous and carries a risk of hypersensitivity.
- **Serum sickness:** a type III hypersensitivity reaction to foreign protein, with fever, urticaria, arthralgia and lymphadenopathy, appearing about one to two weeks after equine serum.

## Matching the product to the exposure

Human-derived products are preferred where they are available, because they carry less risk of hypersensitivity than equine preparations. The table sets out the common products used in Indian practice.

| Product | Source | Typical use |
|---|---|---|
| Human rabies immunoglobulin | Pooled human plasma | Wound infiltration with rabies vaccine |
| Equine rabies immunoglobulin | Immunised horse | Rabies exposure when human product is unavailable |
| Tetanus immunoglobulin | Human plasma | Tetanus-prone wound, uncertain vaccination |
| Hepatitis B immunoglobulin | Human plasma | Exposure, or newborn of an HBsAg-positive mother |
| Anti-D immunoglobulin | Human plasma | Rh-negative mother after an Rh-positive exposure |
| Diphtheria antitoxin | Immunised horse | Treatment of diphtheria |

Equine products are given only after the patient is screened for horse-serum sensitivity, and monitoring for reactions is part of the administration. Timing matters as much as the product. Hepatitis B immunoglobulin for a newborn of an HBsAg-positive mother is most useful when given within about 24 hours of birth, alongside the first vaccine dose. Immunoglobulin supplements vaccination and never replaces it, so the vaccine schedule must still be completed.

## Where the exam tries to catch you

Passive immunisation questions usually test duration, source and the risk of a reaction.

- **Trap:** assuming immunoglobulin gives lasting protection like vaccination — **Correct:** passive antibody wanes over weeks and creates no memory, so a vaccine must follow for lasting protection.
- **Trap:** giving equine antitoxin without screening — **Correct:** horse serum must be tested for hypersensitivity first, because anaphylaxis and serum sickness are the main risks.
- **Trap:** expecting serum sickness immediately after the injection — **Correct:** it appears about one to two weeks later as a type III reaction, not as an immediate anaphylactic event.

## Frequently asked questions

### How long does passive immunity from immunoglobulin last?
Passive immunity from immunoglobulin lasts only a few weeks, because the transferred antibodies are gradually catabolised. Hyperimmune globulin protects during the window before active immunity develops, and vaccination must be completed for lasting protection against the disease.

### Why is equine rabies immunoglobulin given with caution?
Equine rabies immunoglobulin carries a risk of hypersensitivity and serum sickness because it is foreign protein from horses. Monitoring with emergency drugs ready is essential, sensitivity testing is used in some protocols, and human rabies immunoglobulin is preferred whenever it is available.

### When is tetanus immunoglobulin given after a wound?
Tetanus immunoglobulin is given with tetanus toxoid after a tetanus-prone wound when vaccination history is unknown or incomplete. The standard intramuscular dose is 250 IU, given at a site separate from the vaccine injection.

### What is serum sickness and when does it appear?
Serum sickness is a type III hypersensitivity reaction to foreign protein in antiserum, causing fever, urticaria, arthralgia and lymphadenopathy. It usually appears about one to two weeks after heterologous serum is given, and it is managed with antihistamines and, when needed, corticosteroids.