Rabies vaccine is unique in that it is most often used after exposure to the disease. The only people who typically get vaccinated as a preventive measure (before exposure) are those who are at high risk for exposure, such as laboratory workers, veterinarians, animal handlers, spelunkers, and travelers going to parts of the world where exposure to rabies is likely. For these people three doses of vaccine are given; the second is given seven days after the first dose and the third 21 to 28 days after the first dose.
For those who have been exposed to rabies, the vaccine is given to prevent the progressive, invariably fatal disease, rabies. In these situations, a total of four shots are given in the shoulder muscle: The first shot is given immediately after exposure to a rabid animal, then again three days later, seven days later, and 14 days later.
Rabies is deadly
There are only three known cases of unvaccinated people surviving rabies once they developed symptoms of the disease.
- The disease
What is rabies?
Rabies is a virus that attacks the brain and nervous system. It is transmitted by a bite from a rabid animal (meaning an animal infected with rabies virus). The incubation period of the virus, or the time it takes between exposure to the virus and the first symptoms of the disease, is quite long: on average, about two months. Because the virus has a long incubation period, the rabies vaccine works even though it is given after exposure to the virus. However, once the symptoms start, the progression of the disease is relentless and unstoppable.
The first symptoms of rabies are fatigue, sore throat, chills, vomiting and headache. These symptoms get progressively worse a week later with disorientation, hallucinations, unusual behavior, hyperactivity and difficulty swallowing. The final stage of rabies includes paralysis, coma and, ultimately, death.
How do you catch rabies?
Rabies is contracted by exposure to the saliva of an infected animal. Rabies can be transmitted if a bite from an infected animal penetrates the skin. Rabies can also be transmitted if an infected animal licks an open wound, cut or scratch, or if the animal licks the mouth, nose or eyes. Simply petting a rabid animal will not transmit rabies.
If you or a family member is bitten by a rabid animal, you should thoroughly clean the wound and then call the local health department or a local infectious disease expert (in hospitals) to determine which animals in the region are likely to transmit rabies. But generally, in the United States, the following guidelines can serve as a good rule of thumb:
Rabies vaccine is not needed:
- If the animal (for example, dog or cat) lives in or has been hanging around the neighborhood, it can be observed for 10 days to see if it behaves normally.
- If, after 10 days, the animal does not show any signs of rabies, then no treatment is needed.
- Also, animals immunized with the rabies vaccine are unlikely to transmit rabies — all the more reason to make sure that your animals are immunized with rabies vaccine.
Mice, rats, squirrels, rabbits, birds and chipmunks generally do not carry rabies. There has been no record of reptiles, amphibians or fish ever becoming infected with or transmitting rabies.
Rabies vaccine is needed:
- If no one knows the animal and it cannot be observed, or in countries where rabid animals are prevalent, treatment should begin immediately.
- If, within the 10 days of observation, the animal shows any signs of rabies (such as bizarre or unusual behavior), then treatment should begin immediately.
Wild animals, such as raccoons, skunks, foxes, coyotes and bats may carry rabies. Unvaccinated companion animals, such as cats and dogs, may carry rabies.
The Centers for Disease Control and Prevention (CDC) has a map showing the areas of the country in which certain types of animals are considered reservoirs for rabies.
How do you treat someone who is bitten by a potentially rabid animal?
Treatment of people bitten by an animal that might be rabid should include the following:
- Wash the wound carefully with soap and water.
- Administer rabies immune globulin* (this is a preparation of serum obtained from people who have high levels of rabies-specific antibodies in their blood). Rabies immune globulin should be injected in and around the wound to prevent attachment of the rabies virus to the nervous system.
- Begin the series of shots of rabies vaccine immediately.*
- Call animal control authorities.
*Rabies immune globulin and the rabies vaccine are administered in local emergency departments.
- The vaccine
How is the rabies vaccine made?
The rabies vaccine is grown in cells in the laboratory. Three different kinds of cells are used:
- Human cells obtained from a single elective abortion performed in the early 1960s
- Chick embryo cells
- Fetal rhesus lung cells
After the virus is grown in these cells, it is purified away from the cells and treated with a chemical (called beta-propiolactone) that completely kills the virus. The rabies vaccine is, like influenza and hepatitis A vaccines, a "killed" viral vaccine. (see How Are Vaccines Made?).
Does the rabies vaccine work?
The rabies vaccine works remarkably well. Studies indicate that if the vaccine is given immediately and appropriately to someone who was bitten by a rabid animal, it is 100 percent effective.
Does the rabies vaccine have side effects?
Although the rabies vaccine used today does have a fairly high rate of side effects, they are generally mild:
- Sore arm (15 to 25 of 100 recipients),
- Headache (5 to 8 of 100 recipients), or
- Nausea and vomiting (2 to 5 of 100 recipients)
The severe side effect of anaphylaxis has also been reported to follow vaccination in about 1 of every 10,000 doses of vaccine given. This severe allergic reaction includes such symptoms as swelling of the mouth, difficulty breathing, low blood pressure or shock. Anaphylaxis usually occurs within 15 minutes after receiving the vaccine; therefore, it is a good idea to wait in the doctor's office for a little while after receiving the vaccine.
The "old" rabies vaccine versus the "new" rabies vaccine
In the past, the rabies vaccine required as many as 30 shots and was quite painful. The "new" rabies vaccine requires only four shots following a potential exposure to the virus and is much less painful.
- Relative risks and benefits
Do the benefits of the rabies vaccine outweigh the risks?
The rabies vaccine works extremely well to prevent rabies but has a fairly high rate of side effects such as nausea, vomiting and dizziness. The vaccine is also rarely a cause of the severe allergic reaction, anaphylaxis. No one has ever died from the current rabies vaccine. On the other hand, once symptoms have begun, rabies is a uniformly fatal disease. So the benefits of the rabies vaccine clearly outweigh the risks of the vaccine.
- Early symptoms: fatigue, sore throat, chills, vomiting and headache
- Later symptoms: disorientation, hallucinations, unusual behavior, hyperactivity and difficulty swallowing, coma, paralysis
- Untreated disease is uniformly fatal
- Pain at the injection site (Up to 1 of 4 people)
- Headache (Up to 8 of 100 people)
- Nausea and vomiting (Up to 5 of 100 people)
- Anaphylaxis (1 of 10,000 people)
Plotkin SA, Orenstein W, and Offit PA. Rabies vaccines in Vaccines, 6th Edition, 2012, 646-668.