Rabies is a deadly virus, which resides in the saliva of certain animals, who are referred to as “rabid animals”. In the U.S., these include raccoons, bats, foxes, skunks and coyotes. However, in developing countries, these mostly include stray dogs. Biting or scratching by these animals renders a person infected by rabies virus.
Not just bites and scratches, rabies virus can also gain entry through exposure of an existing wound to saliva of infected animal. On entering the bloodstream, the virus travels and infects the brain tissue, producing typical signs and symptoms. Once these symptoms develop, chances of recovery are minimal, and the individual tends to die.
Although fatal, it is a 100% preventable infection and can be easily treated if immediate medical help is sought.
Any infection has a symptom-free period, following the entry of pathogen in the body. Basically, it is the time elapsed between exposure to the pathogen to the appearance of first symptom. This period is known as “incubation period”. Rabies can have an incubation period ranging from 1 week to 1 year.
Initially, rabies virus causes general symptoms which resemble the symptoms of flu, such as
- General weakness or discomfort
If treatment is not sought at this stage of general symptoms, the virus can infect the brain tissue and produce some distressing symptoms, which are described below.
- Abnormal behavior
Once these symptoms have appeared, infected individuals almost always die.
Getting vaccinated by a trained medical professional is the only treatment of rabies. Seek medical help immediately following an animal bite.
What does Rabies Vaccine Consist of?
Rabies vaccine consists of inactivated rabies virus. Basically, the rabies virus is grown in a particular culture of cell or embryo, which is then inactivated with a chemical. The rabies vaccine has come a long way from growing virus in infected rabbit’s spinal cord to infected sheep and goat’s brain.  However, these vaccines caused some adverse reactions and were discontinued. WHO condemns the use of rabies vaccines which contain brain tissue, calling them unsafe. Modern rabies vaccines are derived from the following sources.
1. Human Diploid Cell Vaccine (HDCV)
2. Purified Chick Embryo Cells (PCEC)
These cell-culture and embryonated-egg derived rabies virus is then treated with a chemical, called beta- propiolactone, which kills and inactivates the virus.
How Do Rabies Vaccines Work?
Once the killed inactivated virus is injected in the human body, the body produces antibodies against the virus. These antibodies then kill the rabies virus which has gained entry in the body through animal bite. Therefore, rabies vaccine confers active immunity to the individual.
How Are Rabies Vaccines Administered?
Rabies vaccine is usually administered intramuscularly. However, it may also be given intradermally, except in cases when patient is on anti-malarial drugs as these drugs may reduce the efficiency of vaccine given intradermally. In adults, the vaccine is usually given in the uppermost part of the arm (medically known as deltoid area). Children younger than 1 year of age should receive the vaccine in the front part of thigh. An important fact here is that rabies vaccine should never be given in the buttocks (medically known as gluteal region).
Pre- Exposure and Post-Exposure Vaccination
Rabies vaccine not just forms a mainstay of treatment of rabies but can also impart protection against the infection in high-risk people. A notable fact is that, whether being used for prevention (pre-exposure vaccination) or post-bite treatment (post-exposure vaccination), similar vaccine is used. However, the difference lies in the frequency of receiving the vaccination (i.e., immunization schedule) and use of an additional rabies immunoglobulin in post-bite treatment. WHO lays down certain recommendations for both these clinical situations, which are described below. 
1. Pre- exposure Vaccination
This aims at preventing the onset of rabies infection in people who are at a high-risk of developing it but have not been bitten by a rabid animal. These high-risk people include the following.
- Wildlife officers
- Animal handlers
- Laboratory workers involved with rabies virus
- People traveling to rabies-affected areas
- People traveling to remote isolated areas with limited accessibility to medical facilities or where locally developed unsafe or ineffective vaccines are available
Immunization Schedule of Pre-exposure Vaccination
Three doses of rabies vaccine are given in pre-exposure cases. First dose is taken as per the need of the individual. Subsequent doses are taken 1 week later and then 21 or 28 days after the 1st dose.
2. Post-exposure vaccination
This refers to vaccinating an individual who has been exposed to the saliva of an animal suspected to have rabies. The exposure can be either through a bite, scratch or any other mode of contact of human mucosa to the virus. Although it shares the same vaccination as is given in pre-exposure vaccination, post-exposure prophylaxis has an added element in the treatment, known as rabies immunoglobulin.
Human Rabies Immunoglobulin (HRIG)
It is not similar to cell-culture or embryonated- egg derived rabies vaccination, mentioned above. Difference lies in the mechanism of action. While rabies vaccine prompts an individual’s immunity to produce antibodies (active immunity), HRIG is a pre-formulated antibody against rabies virus (passive immunity). It must be remembered that HRIG is not the sole treatment of rabies. It is given along with rabies vaccination.
HRIG is mostly reserved for patients having extensive severe exposure to rabies virus, which cannot be treated with just a rabies vaccination. These individuals include those who have single or multiple bites or scratches or animal licks on broken skin. These also include people whose mucous membrane (like lips, mouth, lining of nasal passage, eyes, etc.) have been licked by animal. Another group of people included are those who have been exposed to bats.
HRIG is usually administered at or around the wound site. It is also administered in the muscles, at a site distant from the site of rabies vaccine. Multiple injections in the wounded area is not recommended. If the correct dose of HRIG is too little for an extensive wound, HRIG can be diluted in buffered saline to cover a wider area of wound.
WHO lists down following measures to follow, if an animal has bitten you.
I. Wound Treatment
Immediately following an animal bite, wash the wound with soap/ detergent. Then, apply ethanol or povidone iodine solution.
After washing the wound thoroughly, get yourself vaccinated with rabies vaccination. However, in some cases, a rabies immunoglobulin is also given.
Immunization Schedule of Post-exposure Vaccination
After an animal bite, two immunizations are needed- Rabies vaccination and Rabies immunoglobulin. Details of when should these be given, are mentioned below.
A. Rabies Vaccination
This is given in the muscles (intramuscularly) or in the skin (intradermally). The regimen for intramuscular and intradermal regimens are different, as described below.
i) Intramuscular Regimen
There are two regimens for this vaccination, which are as follows.
- Five-dose Regimen: This included giving 5 doses of rabies vaccination, on 5 separate days. First dose is given on the day of animal bite. This is followed by rabies vaccination on 3rd day, 7th day, 14th day and 28th day following the first dose.
- Four-dose Regimen: This includes giving 4 doses of rabies vaccination, which are divided in only 3 days, i.e., first two doses are given on the day of animal bite (one on left arm and other on right arm). This is followed by giving remaining two doses on 7th day and 21st day after the first dose.
ii) Intradermal Regimen
Intramuscular rabies vaccine is not very cost-effective. Hence, some developing countries may not be able to afford it and may resort to a more economic intradermal rabies vaccine. The regimen used is described below.
- The Two-site Intradermal Method: This method advocates use of one intradermal rabies vaccine in two sites, on 4 separate days. First dose is given on the day of animal bite. This is followed by giving the vaccine on 3rd day, 7th day and 28th day after the first dose.
B. Human Rabies Immunoglobulin (HRIG)
HRIG is usually given either before or shortly after giving rabies vaccination. As per WHO guidelines, HRIG can be given up to 7th day from giving the first dose of rabies vaccination.
Common Brand Names of Rabies Vaccination
Imovax and RabAvert are the U.S.FDA approved brands of Rabies vaccine.
Rabies vaccine may cause some adverse reaction, which are as follows.
- Pain, erythema and swelling at the injection site
- Abdominal pain
- Muscle aches
Safety in Pregnancy
Pre-exposure rabies vaccine should be given in pregnancy only if benefit outweighs fetal risk. However, if a pregnant women is exposed to the virus, post-exposure vaccination must be given.
Rabies vaccine does not contain alcohol.
Rabies vaccine is not available over the counter. If you are at a high-risk of acquiring rabies or have been bitten by an animal suspected of rabies, you must seek medical help immediately. Delaying the treatment may cause the virus to invade brain tissue, which almost always leads to death. Also, vaccinations must be received by a trained health care professional.