What is rabies immunoglobulin?
Rabies immunoglobulin (RIG) is a preparation of ready-made antibodies against the rabies virus. Unlike the vaccine — which teaches the immune system to make its own antibodies over 1–2 weeks — RIG provides immediate ("passive") protection right at the wound site, covering the gap before the vaccine-induced ("active") immunity takes over. The two work together, not as alternatives: RIG neutralises virus in and around the bite before it can travel to nerve tissue, while the vaccine builds the lasting immune response.
There are two types in use worldwide:
- Human RIG (HRIG): purified from pooled human plasma. Preferred where available — lower dose (20 IU/kg), no risk of serum sickness.
- Equine RIG (ERIG): purified F(ab')2 fragments from horse serum. Effective and widely used where HRIG is unavailable or cost-prohibitive, at double the dose (40 IU/kg) — modern purified ERIG has a low but non-zero rate of hypersensitivity reactions.
How the RIG dose is calculated
RIG is only given once, at the start of PEP (ideally Day 0) — never repeated at later vaccine visits.
Vaccination and RIG by exposure category
Both the vaccine course and RIG eligibility are determined by the same WHO/NCDC exposure category — RIG is never given alone, and is only ever added on top of the full vaccine course, never in place of it.
| Category | Exposure | Vaccine | RIG |
|---|---|---|---|
| I | Touching or feeding animals; licks on intact skin | Not required | Not required |
| II | Nibbling of uncovered skin; minor scratches or abrasions without bleeding | Full course required (see ARV Scheduler) | Not required |
| III | Transdermal bites/scratches, licks on broken skin, mucosal contamination, or any bat contact | Full course required (see ARV Scheduler) | Required, if not previously vaccinated |
Regardless of category, a patient who is already fully, previously vaccinated only ever needs the abbreviated 2-visit booster schedule and never needs RIG.
Clinical use
- Infiltrate the wound first: as much of the calculated dose as anatomically possible should be infiltrated into and around all wounds; only inject any leftover volume intramuscularly at a site distant from the vaccine.
- Never mix RIG and vaccine in the same syringe or site: they're always given at separate sites.
- Human vs equine choice: human RIG (HRIG) is preferred where available — lower dose, no serum sickness risk. Equine RIG (ERIG, purified F(ab')2) is a widely used, effective alternative where HRIG is unavailable or cost-prohibitive, at double the IU/kg dose.
- Vaccination route is independent of RIG: whether the accompanying vaccine course is given IM (Essen) or ID (updated Thai Red Cross) doesn't change the RIG dose itself — it's tracked here only to keep the record consistent with the linked ARV schedule.
Frequently asked questions
What is rabies immunoglobulin (RIG)?
It's a preparation of ready-made antibodies against rabies virus, given once at the start of post-exposure treatment to provide immediate protection while the vaccine course builds the body's own longer-lasting immunity.
What's the difference between RIG and the rabies vaccine?
RIG is passive immunity — ready-made antibodies that act immediately but wear off over time. The vaccine is active immunity — it takes 1–2 weeks to build a response, but that response lasts. They're given together for Category III exposures precisely because RIG covers the gap before the vaccine takes effect.
Is RIG needed for a Category I exposure?
No. Category I (touching or feeding an animal, or licks on intact skin) carries no risk of rabies transmission — wash the area and no vaccine or RIG is needed at all.
Is RIG needed for a Category II exposure?
No. Category II (minor scratches or nibbles without bleeding) needs the full vaccine course, but not RIG — RIG is reserved for Category III exposures.
What's the difference between human and equine RIG?
Human RIG (HRIG) is purified from human plasma, dosed at 20 IU/kg, and carries no serum-sickness risk — it's preferred where available. Equine RIG (ERIG) is a purified horse-serum product, dosed at 40 IU/kg (double), and is an effective, widely used alternative where HRIG isn't available or affordable, with a low but real rate of hypersensitivity reactions.
Can RIG be given after the vaccine course has already started?
Yes, but only within the first 7 days after the first vaccine dose. After that window, the patient's own active immune response should already be developing, and giving RIG that late can actually blunt the vaccine's effect.
Do previously vaccinated people need RIG?
No — if someone has a documented complete prior rabies vaccination course, they only need the abbreviated 2-visit booster schedule on re-exposure, and never need RIG, regardless of the exposure category.
What are the side effects of RIG?
Local pain, redness, or mild swelling at the infiltration site are common. Human RIG rarely causes systemic reactions. Equine RIG carries a low rate of hypersensitivity/serum-sickness-type reactions with modern purified products — anaphylaxis is rare but facilities giving ERIG should be prepared to manage it.
How is the RIG dose calculated?
By body weight: 20 IU per kg for human RIG, or 40 IU per kg for equine RIG. The full calculated dose is infiltrated into and around the wound(s), with any remaining volume given intramuscularly at a site away from the vaccine injection.
References
- National Centre for Disease Control (NCDC), Directorate General of Health Services, Ministry of Health & Family Welfare, Government of India. National Guidelines on Rabies Prophylaxis, 2019.
- World Health Organization. WHO position paper on rabies vaccines. Wkly Epidemiol Rec. 2018;93(16):201–219.
- World Health Organization. Rabies vaccines and immunoglobulins: WHO position — updated guidance, 2018.