Rabies vaccine

The World Health Organization (WHO) recommends vaccinating those who are at high risk of the disease, such as children who live in areas where it is common.[6] Other groups may include veterinarians, researchers, or people planning to travel to regions where rabies is common.[9] Three doses of the vaccine are given over a one-month period on days zero, seven, and either twenty-one or twenty-eight.[6][9]

For individuals who have been potentially exposed to the virus, four doses over two weeks are recommended, as well as an injection of rabies immunoglobulin with the first dose.[10] This is known as post-exposure vaccination.[11] For people who have previously been vaccinated, only a single dose of the rabies vaccine is required.[11] However, vaccination after exposure is neither a treatment nor a cure for rabies; it can only prevent the development of rabies in a person if given before the virus reaches the brain.[11] Because the rabies virus has a relatively long incubation period, post-exposure vaccinations are typically highly effective.[6]

Immunity following a course of doses is typically long lasting, and additional doses are usually not needed unless the person has a high risk of contracting the virus.[6] Those at risk may have tests done to measure the amount of rabies antibodies in the blood, and then get rabies boosters as needed.[9] Following administration of a booster dose, one study found 97% of immunocompetent individuals demonstrated protective levels of neutralizing antibodies after ten years.[12]

Aside from vaccinating humans, another approach was also developed by vaccinating dogs to prevent the spread of the virus. In 1979, the Van Houweling Research Laboratory of the Silliman University Medical Center in Dumaguete in the Philippines[22] developed and produced a dog vaccine that gave a three-year immunity from rabies. The development of the vaccine resulted in the elimination of rabies in many parts of the Visayas and Mindanao Islands. The successful program in the Philippines was later used as a model by other countries, such as Ecuador and the Yucatan State of Mexico, in their fight against rabies conducted in collaboration with the World Health Organization.[23]

In Tunisia a rabies control program was initiated to give dog owners free vaccination to promote mass vaccination which was sponsored by their government. The vaccine is known as Rabisin (Mérial), which is a cell based rabies vaccine only used countrywide. Vaccinations are often administered when owners take in their dogs for check-ups and visits at the vet.[24]

Wildlife species, primarily bats, raccoons, skunks, and foxes, act as reservoir species for different variants of the rabies virus.[13][25] This results in the general occurrence of rabies as well as outbreaks in animal populations.[25] Approximately 90% of all reported rabies cases in the US are from wildlife.[25]

There is an oral vaccination in pellet form which can be left out for wild animals to produce a herd immunity effect.[26] Oral rabies vaccination (ORV) programs have been used in many countries in an effort to control the spread of rabies and limit the risk of human contact with the rabies virus.[25] ORV programs were initiated in Europe in the 1980s, Canada in 1985, and in the United States in 1990.[27] ORV is a preventive measure to eradicate rabies in wild animal vectors of disease, mainly foxes, raccoons, raccoon dogs, coyotes and jackals, but also can be used for dogs in developing countries.[28] ORV programs typically use edible baits to deliver the vaccine to targeted animals. ORV baits consist of a small packet containing the oral vaccine which is then either coated in a fishmeal paste or encased in a fishmeal-polymer block.[25] When an animal bites into the bait, the packets burst and the vaccine is administered.[27] Current research suggests that if adequate amounts of the vaccine is ingested, immunity to the virus should last for upwards of one year.[29] By immunizing wild or stray animals, ORV programs work to create a buffer zone between the rabies virus and potential contact with humans, pets, or livestock.[27] The effectiveness of ORV campaigns in specific areas is determined through trap-and-release methods.[30] Titer tests are performed on the blood drawn from the sample animals in order to measure rabies antibody levels in the blood.[30] Baits are usually distributed by aircraft to more efficiently cover large, rural regions. In order to place baits more precisely and to minimize human and pet contact with baits, however, they are distributed by hand in suburban or urban regions.[27] The potential for human contact with baits is a present concern for OPV programs, but the oral vaccine does not contain the whole rabies virus and has been proven safe in over 60 animal species including cats and dogs.[29] The idea of wildlife vaccination was conceived during the 1960s, and modified-live rabies viruses were used for the experimental oral vaccination of carnivores by the 1970s. The development of safe and effective rabies virus vaccines applied in attractive baits resulted in the first field trials in Switzerland in 1978 to immunize red foxes.[31] ORV programs have seen success in preventing the westward spread of raccoon variant rabies in the United States and even eradicating rabies in red foxes in Switzerland.[32][33]

Imrab is an example of a veterinary rabies vaccine containing the Pasteur strain of killed rabies virus. Several different types of Imrab exist, including Imrab, Imrab 3, and Imrab Large Animal. Imrab 3 has been approved for ferrets and, in some areas, pet skunks.[34][35] The reason why these oral vaccines that enter the body through the GI tract are able to convey resistance to rabies is due to the usage of a live human adenovirus type 5 vector. Adenovirus, a common viral pathogen that infects the GI tract and causes diarrhea is genetically altered to express rabies surface proteins, thereby allowing the adenovirus to infect GI tract cells. This enables the viral vector to infect cells in the GI and stimulate a cellular and humoral response that would provide immunity in the case of being bitten by an infected animal and being infected via blood.