Vaccines

Understanding the Disease

Rabies is an acute and deadly disease caused by a viral infection of the central nervous system. The rabies virus is most often spread by a bite and saliva from an infected (rabid) animal (e.g., bats, raccoons, skunks, foxes, ferrets, cats, or dogs). In the United States, rabies is most often associated with bat exposures. However, there have been rare cases in which laboratory workers and explorers in caves inhabited by millions of bats were infected by rabies virus in the air.

Virtually 100% of those infected with rabies who do not receive the vaccine will die. Rabies illness includes rapidly progressing central nervous system symptoms such as anxiety, difficulty swallowing, and seizures.

Although less than ten human rabies fatalities occur in the United States annually, as many as 40,000 Americans receive the vaccine each year after contact with animals suspected of being rabid. An additional 18,000 people get the vaccine before exposure as a preventative measure.

Worldwide, at least 4 million people are vaccinated each year for rabies. The number of deaths that rabies causes each year is estimated to be at least 40,000, and as high as 70,000 if higher case estimates are used for densely populated countries in Africa and Asia where rabies is epidemic. India, with a very large population of stray, ownerless dogs, has about half of all cases of rabies worldwide. Between 30-60% of human rabies cases occur in children under 15 years of age.

Prompt wound care and the administration of rabies immune globulin (RIG) plus vaccine are highly effective in preventing human rabies following exposure.

Available Vaccines

The rabies vaccine is available as:

• Human diploid cell vaccine (HDCV)
• Purified chick embryo cell vaccine (PCECV)

Product: Imovax Rabies (HDCV for pre or post-exposure)
Manufacturer: Sanofi Pasteur
Year Licensed: 1980

Product: RabAvert (PCECV for pre or post-exposure)
Manufacturer: Novartis
Year Licensed: 1997

History of the Vaccine

The first rabies vaccine was developed in the early 1960’s. All rabies vaccines currently available for humans are made from killed rabies virus.

Who Should and Should Not Receive the Vaccine

Who should receive the vaccine pre-exposure?

• Vaccination before exposure (pre-exposure) should be offered to people in high risk groups such as veterinarians, animal handler/caretakers, or laboratory workers who may be exposed to the rabies virus.

Pre-exposure vaccination may be considered for:

• People whose activities bring them into frequent contact with rabies virus or potentially rabid animals (e.g., bats, raccoons, skunks, ferrets, cats, dogs).
• Travelers who will spend more than one month in countries with a high rate of rabies infection, if they are likely to come in contact with rabid animals and immediate access to appropriate medical care is limited.

Who should receive the vaccine post-exposure?

• Vaccination after exposure (post-exposure) is recommended for all individuals who have had contact with an animal (e.g., bites or abrasions) that they believe may be, or which is proven to be, rabid. Vaccination should be initiated as soon after exposure as possible and should be accompanied by proper wound management and the administration of Rabies Immune Globulin, human (HRIG).

Pregnant women who are exposed to rabies may receive the vaccine.

 

Who should not receive the vaccine?

• The rabies vaccines are not recommended for routine use.
• People who are moderately or severely ill should consult with their physician before receiving any vaccine.

Dose Schedule

Pre-exposure rabies vaccines are administered by a series of three injections:

• The first dose may be given at any time
• The second dose should be given seven days later
• The third dose should be given 21 or 28 days after the first dose
• Booster doses of vaccine are recommended every two years for those individuals who continue to be at increased risk of contracting rabies to maintain protective antibody levels. People that work with live rabies virus in laboratory settings should be tested every six months to ensure that they have adequate antibody levels, and receive boosters as necessary.

When post-exposure rabies vaccines are administered:

• The number of doses required is determined by the previous immunization status of the individual
• Previously unvaccinated people should receive the vaccine intramuscularly at 0, 3, 7, and 14  days. For adults the vaccine is given in the deltoid area; for children, it may be given in the anterolateral aspect of the thigh. In addition to rabies vaccine, these people should also receive rabies immune globulin (HRIG) at the same time as the first dose of the vaccine to provide rapid protection that persists until the vaccine works.
• Previously vaccinated people should receive two doses of the vaccine intramuscularly—the first immediately, the other three days later. RIG is unnecessary and should not be given. An immunized person is anyone who has received a complete series of vaccine, or a person who has received a pre-exposure or post-exposure series of any rabies vaccine who has an adequate rabies antibody level.

Effectiveness of the Vaccine

There are no controlled trials of rabies vaccine. Among persons who had been bitten by an animal that was proven to be rabid and who received both HRIG and a full course of one of these modern rabies vaccines there have been no cases of rabies. Previously immunized people still must receive two additional doses of the vaccine if exposed to the virus, and the vaccine is almost 100% effective in these cases as well.

Although all rabies vaccines licensed in the U.S. induce protective antibody levels after three doses in nearly 100% of recipients, it is important to complete the dose schedules recommended for individual circumstances (see Dose Schedule). Previously, a 5-dose vaccine schedule was recommended but the dose that was given at 28 days is no longer felt to be necessary.

Known Side Effects

Mild reactions such as pain, redness, swelling, or itching at injection site are reported among 30%-74% of those vaccinated. Headache, nausea, abdominal pain, muscle aches, and dizziness are reported in 5-40% of those vaccinated.

Serious events after vaccination are rare. However, allergic reactions including swelling and mild difficulty breathing developed in 6% of patients who received booster doses of Human Diploid Cell Rabies Vaccine. In addition, three cases of neurologic illness resembling Guillain-Barré Syndrome, a progressive disorder affecting the nervous system, have been reported in people who received the Human Diploid Cell Rabies Vaccine. In these cases, all patients recovered within three months.

This vaccine is recommended by:

• Advisory Committee of Immunization Practices of the Centers for Disease Control and Prevention
• American Academy of Pediatrics
• American Thoracic Society

Related Issues

What should you do if bitten by a rabid or suspicious animal?

1) Wash all bites and scratches immediately and thoroughly with soap and water and a solution that kills viruses (such as a povidone-iodine solution). Wound cleansing alone will markedly reduce the chances of getting rabies.
2) Go to a health care provider for a medical assessment regarding the need for a tetanus shot (if it needs to be updated), rabies vaccination, and administration of RIG, human. Two rabies immune globulins are licensed for use in the U.S. Each year approximately 18,000 people in the U.S. receive vaccination and immune globulin, and none of them has developed rabies.
3) Notify the state or local health department.

Vaccination and appropriate immune globulin therapy can protect you after you have been bitten. Vaccination before exposure merely simplifies therapy by eliminating the need for RIG and decreasing the number of vaccine doses needed.

Effective rabies control measures include routine immunization of dogs, cats, and ferrets, and control of stray dogs and selected wildlife. A fully vaccinated dog or cat is unlikely to become infected or to transmit rabies.

Key References and Sources of Additional Information

• Centers for Disease Control and Prevention (CDC). (2008). Human rabies prevention—United States,2008: Recommendations of the Advisory Commission on Immunization Practices (ACIP). Morbidity and Mortality Weekly Report, 57(RR-3).
• Centers for Disease Control and Prevention (CDC). (2010). Use of a reduced (4-dose) vaccine schedule for postexposure prophylaxis to prevent human rabies: Recommendations of the Advisory Commission on Immunization Practices (ACIP). Morbidity and Mortality Weekly Report, 59(RR-2) .