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Rabies

Vaccine

Vaccination against rabies is used in two distinct situations:

• to protect those who are at risk of exposure to rabies, i.e. pre-exposure vaccination;
• to prevent the development of clinical rabies after exposure has occurred, usually following the bite of an animal suspected of having rabies, i.e. postexposure prophylaxis.

The vaccines used for pre-exposure and post-exposure vaccination are the same, but the immunization schedule differs. Rabies immunoglobulin is used only for post-exposure prophylaxis. Modern vaccines of cell-culture or embryonated-egg origin are safer and more effective than the older vaccines, which were produced in brain tissue. These modern rabies vaccines are now available in major urban centres of most countries of the developing world. Rabies immunoglobulin, on the other hand, is in short supply worldwide and may not be available, even in major urban centres, in many dog rabiesinfected countries.

Pre-exposure vaccination

Pre-exposure vaccination should be offered to people at high risk of exposure to rabies, such as laboratory staff working with rabies virus, veterinarians, animal handlers and wildlife officers, and other individuals living in or travelling to countries or areas at risk. Travellers with extensive outdoor exposure in rural areas – such as might occur while running, bicycling, hiking, camping, backpacking, etc. – may be at risk, even if the duration of travel is short. Pre-exposure vaccination is advisable for children living in or visiting countries or areas at risk, where they provide an easy target for rabid animals. Pre-exposure vaccination is also recommended for individuals travelling to isolated areas or to areas where immediate access to appropriate medical care is limited or to countries or areas where modern rabies vaccines are in short supply and locally available rabies vaccines might be unsafe and/or ineffective.

Pre-exposure rabies vaccination consists of three full intramuscular doses of cell-culture- or embryonated-egg-based vaccine given on days 0, 7 and 21 or 28 (a few days’ variation in the timing is not important). For adults, the vaccine should always be administered in the deltoid area of the arm; for young children (under 1 years of age), the anterolateral area of the thigh is recommended. Rabies vaccine should never be administered in the gluteal area: administration in this manner will result in lower neutralizing antibody titres.

To reduce the cost of cell-derived vaccines for pre-exposure rabies vaccination, intradermal vaccination in 0.1-ml volumes on days 0, 7 and either 21 or 28 may be considered. This method of administration is an acceptable alternative to the standard intramuscular administration, but it is technically more demanding and requires appropriate staff training and qualified medical supervision. Concurrent use of chloroquine can reduce the antibody response to intradermal application of cell-culture rabies vaccines. People who are currently receiving malaria prophylaxis or who are unable to complete the entire three-dose pre-exposure series before starting malarial prophylaxis should therefore receive pre-exposure vaccination by the intramuscular route.

Periodic booster injections are therefore not recommended for general travellers. However, in the event of exposure through the bite or scratch of an animal known or suspected to be rabid, individuals who have previously received a complete series of pre- or post-exposure rabies vaccine (with cell-culture or embryonated-egg vaccine) should receive two booster doses of vaccine. Ideally, the first dose should be administered on the day of exposure and the second 3 days later. This should be combined with thorough wound treatment (see “Post-exposure prophylaxis”, below). Rabies immunoglobulin is not required for previously vaccinated patients.

Precautions and contraindications

Modern rabies vaccines are well tolerated. The frequency of minor adverse reactions (local pain, erythema, swelling and pruritus) varies widely from one report to another. Occasional systemic reactions (malaise, generalized aches and headaches) have been noted after both intramuscular and intradermal injections.

Post-exposure prophylaxis

In countries or areas at risk of rabies, the circumstances of an animal bite or other contact with an animal suspected to be rabid may require postexposure prophylaxis. In such situations, medical advice should be obtained immediately.

Strict adherence to the WHO-recommended guidelines for optimal post-exposure rabies prophylaxis virtually guarantees protection from the disease. The administration of vaccine, and immunoglobulin if required, must be conducted by, or under the direct supervision of, a physician. Post-exposure prophylaxis depends on the type of contact with the confirmed or suspect rabid animal, as follows:

^a Exposure to rodents, rabbits and hares seldom, if ever, requires specific anti-rabies post-exposure prophylaxis.

^b If an apparently healthy dog or cat in or from a low-risk country or area is placed under observation, the situation may warrant delaying initiation of treatment.

^c This observation period applies only to dogs and cats. Except in the case of threatened or endangered species, other domestic and wild animals suspected to be rabid should be humanely killed and their tissues examined for the presence of rabies antigen using appropriate laboratory techniques.

^d Post-exposure prophylaxis should be considered for individuals who have been in close contact with bats, particularly following bites or scratches or exposure to mucous membranes.

1. Wound treatment

Thorough washing of the wound with soap/detergent and water, followed by the application of ethanol or an aqueous solution of iodine or povidone.

2. Passive immunization

Human rabies immunoglobulin (HRIG) or equine rabies immunoglobulin (ERIG) or F(ab’)2 products for category III exposures as well as some category II exposures (see table, above). Passive immunization should be administered just before or shortly after administration of the first dose of vaccine given in the post-exposure prophylaxis regimen. If it is not immediately available, passive immunization can be administered up until the seventh day after initiation of the primary series of post-exposure prophylaxis (with cell-culture or embryonated-egg rabies vaccine).

Dosage and administration: The dose for HRIG is 20 IU/kg body weight and for ERIG and F(ab’)2 products 40 IU/kg body weight. The full dose of rabies immunoglobulin, or as much as is anatomically feasible, should be administered into and around the wound site. Any remainder should be injected i.m. at a site distant from the site of active vaccine administration. Multiple needle injections into the wound should be avoided. If the correct dose of rabies immunoglobulin is too small to infiltrate all wounds, as might be true of a severely bitten individual, it can be diluted in physiological buffered saline to ensure greater wound coverage.

3. Active immunization

Cell-culture- or embryonated-egg-based rabies vaccines should always be used for post-exposure prophylaxis. They can be administered either i.m. or i.d.

Intramuscular regimens: Both a five-dose and a four-dose i.m. regimen are recommended for post-exposure vaccination; the five-dose (“Essen”) regimen is the more commonly used:

• The five-dose regimen is administered on days 0, 3, 7, 14 and 28 into the deltoid muscle.
• The four-dose regimen is administered as two doses on day 0 (one dose in the right and one in the left deltoid), and then one dose on each of days 7 and 21 into the deltoid muscle.

An alternative post-exposure regimen for healthy, fully immunocompetent exposed people who receive wound care plus high-quality rabies immunoglobulin plus WHO-prequalified rabies vaccines consists of four doses administered i.m. on days 0, 3, 7 and 14.

Intradermal regimens: Intradermal administration of cell-culture- and embryonated- egg-based rabies vaccines has been successfully used in many developing countries that cannot afford the five- or four-dose i.m. schedules.

• The two-site i.d. method: one i.d. injection at two sites on days 0, 3, 7 and 28.

For use with: 0.1 ml for purified Vero cell rabies vaccine; 0.1 ml for purified chick embryo rabies vaccine.