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Introduction and General Information

Vaccination is commonly employed in the prevention and control of viral diseases and vaccines have been developed for protection against some flavivirus diseases.

Until recently, WNV infection was recorded mainly as a mild disease or an inapparent infection in humans while outbreaks of WNV encephalitis in horses were seen only rarely and at widely divergent locations. For this reason there was no apparent need for a WNV vaccine. (J64.19.w1, B242.w1, B244.w1)

This situation has changed in the last few years (J64.19.w1). The recent increase in reports of WNV encephalitis outbreaks in humans and horses, together with the introduction of WN virus into the Western Hemisphere and the occurrence of clinical disease in birds, has given new momentum to vaccine research. (J133.951.w5, J133.951.w26, J133.951.w27, W27.12Mar2002.wnv1)

Published Guidelines linked in Wildpro

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Vaccination of Humans

As of May 2008, no WN Virus vaccines have been developed and licensed for use in humans.
  • Older people have been recognised as a group at particular risk of encephalitis and high mortality associated with WNV infection. Therefore if a vaccine were developed and licensed for use in humans it would be most likely to be used for the protection of the elderly in targeted geographical regions where WNV infection epidemics were considered likely, or in the face of such an epidemic. 
  • It has also been suggested that vaccination may be useful if large numbers of non-immune humans were moving into an area known to have a very high rate of transmission of WN virus. 

(J84.7.w14, J84.7.w32, J98.352.w1, J129.42.w1, J133.951.w5, B241.49.w49, B244.w1)

Work on vaccines has intensified in the last few years and some promising advances have been made. 

  • At least two vaccine manufacturers are working on the development of chimeric vaccines, in which WN Virus structural proteins replace the structural proteins in a related virus, for use in humans. (J133.951.w5, J135.99.w1, W27.12Mar2002.wnv1).
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Vaccination of Horses

Data from studies of both natural infections and experimental challenges with virulent WN virus has shown that vaccination is effective in protecting horses against development of viraemia, clinical disease and severe clinical disease resulting in death or euthanasia. (J4.225.w2, J4.225.w3, J4.228.w1, J14.48.w2, J87.39.w3, J484.38.w1, P51.51.w1) In one study it was noted that the costs of a vaccination course (two doses of vaccine) was about 1/45th the cost of treating a clinical case of WNV infection in a horse. (J484.38.w1) Vaccination should be used together with integrated mosquito control. (P51.49.w3)
Vaccines available

Three vaccines against WN virus have been licensed for use in horses in the USA and Canada and are available commercially; a fourth vaccine has also been granted a license by USDA but is not commercially available [data to May 2008]: (J4.229.w2, J87.39.w3, J89.22.w1, J219.14.w2, W30.May08.w1, W43.May08.w1)

  • A killed vaccine (West Nile - Innovator, Fort Dodge Animal Health) has been licensed by the USDA Center for Veterinary Biologics for use in horses in the USA (P39.4.w4) and is also licensed for use in horses in Canada. (W43.May08.w1)
    • This killed vaccine is given intramuscularly (1.0 ml of vaccine) with a booster given three to six weeks later. Following the initial course a booster could be given every year or, in areas at high risk, as frequently as every four to six months. (W30.Nov01.WNV3, J4.219.w1, J4.219.w2)
    • It has been confirmed by APHIS that the killed vaccine is safe to use (following publication of misleading articles suggesting otherwise), and a study has confirmed safety in pregnant mares. (J4.225.w4, W30.28Jan04.WNV2)
    • For further details see: West Nile Virus Disease - Vaccine Developments (Viral Reports)
  • A recombinant vaccine in a canarypox virus vector (RECOMBITEK® Equine West Nile Virus vaccine, Merial Animal Health Ltd.) has been licensed by the USDA Center for Veterinary Biologics for use in horses in the USA (W348.20Jan03.wnv1, W479.Jan04.wnv2) and is also licensed for use in horses in Canada. (W43.May08.w1)
    • Two doses are given by intramuscular injection, four to six weeks apart, followed by an annual booster. (D150)
  • A live flavivirus chimera vaccine (PreveNile, Intervet) has been licensed by USDA for use in horses in the USA (J4.229.w2) and is also licensed for use in horses in Canada. (W43.May08.w1)
    • A single dose is given by intramuscular injection for primary immunization, in horses of five months old or older, followed by an annual booster. (W496.May08.w1)
  • A DNA vaccine from Fort Dodge Animal Health was granted a license by USDA in July 2005 (J89.22.w1, W30.May08.w1); this is not commercially available. (J219.14.w2)
Vaccine recommendations
  • NOTE: It has been recommended by APHIS (USDA) that owners both vaccinate their horses against WN virus and also take measures to avoid exposure of their animals to mosquitoes. (W30.28Jan04.WNV2) See: Personal Protection for West Nile Virus - Individual Protection for Horses

Recommendations from AAEP regarding WN Virus vaccination are [May 2008]: (W246.May08.w1)

  • Foals from vaccinated mares: 
    • Inactivated vaccine - a course of three doses, starting at four to six months, with the second dose four to six weeks later and a third dose at 10 - 12 months, before the onset of the mosquito season.
    • Recombinant canarypox vaccine - no data is available, but assuming response of foals is similar to that of adults, vaccination could start at 5 - 6 months of age with the second dose four weeks later and a third dose at 10 - 12 months, before the onset of the mosquito season. 
    • Modified live chimera vaccine - no data is available for younger foals, but it is licensed for use in foals of five months of age or older, with a single dose and then the first booster when the animals is 10 - 12 months old, before the onset of the next mosquito season. 
  • Foals from unvaccinated mares: 
    • The primary course may be started when the foal is three months old and ideally should be completed before the onset of the mosquito season.
    • Inactivated vaccine - a course of three doses, starting at three months, with the second dose 30 days later and the third dose 60 days (eight weeks) after the second dose, or just 3-4 weeks after the second dose if during the active mosquito season. 
    • Recombinant canarypox vaccine - no data is available, but assuming response of foals is similar to that of adults, vaccination could start at 5 - 6 months of age with the second dose three to four weeks later. 
    • Modified live chimera vaccine - no data is available regarding use of this vaccine in foals under five months of age. 
  • Adults previously vaccinated: 
    • Re-vaccinate previously-vaccinated individuals annually in spring before onset of the mosquito season.
    • If a horse is at high risk or has limited immunity, more frequent vaccination may be considered - e.g. for horses over 15 years of age, and for juveniles less than five years of age.
  • Adults not previously vaccinated:
    • Inactivated vaccine - Primary course of two doses four to six weeks apart. Following this, "The label recommended revaccination interval is 12 months."
    • Recombinant canarypox vaccine - Primary course of two doses four to six weeks apart. Following this, "The label recommended revaccination interval is 12 months."
    • Modified live chimera vaccine - Primary course of a single immunization in horses five months old or older. Following this, "The label recommended revaccination interval is 12 months.".
  • For broodmares: 
    • Vaccination has not been shown to be associated with increased loss of pregnancy.
    • For broodmares previously vaccinated - Vaccination at four to six weeks prepartum. (W246.May08.w1) This may be useful to boost immunity and increase passive immunity of foals via antibodies in colostrum. (W246.May08.w2)
    • For broodmares not previously vaccinated - start vaccination immediately; although "vaccinanation of naive mares while open is a preferred strategy."

(W246.May08.w1)

Note: vaccinated animals might not meet the import requirements of other countries due to the presence of certain antibodies in the blood. (J4.219.w1)
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Vaccination of Birds

In the USA: No WN virus vaccines have been developed and licensed at the present time [May 2008] for use in birds in the USA.
  • There might be a limited role for such a vaccine in the protection of commercial goose flocks and/or rare or endangered bird species in captive collections which are known or feared to be susceptible to this disease. 
  • Vaccination of free-ranging wild birds such as corvids (Corvidae) in order to protect them, or wider vaccination to reduce the availability of naive amplifier hosts for the virus (as in oral vaccination against rabies in foxes in many areas of Europe), is not practical at the present time with available vaccines.
  • Birds of various species have been vaccinated using the killed-virus vaccine developed for use in horses (e.g. at the National Zoo, Washington DC, Houston Zoo, Texas and Toronto Zoo, Canada). (P9.2004.w13, W27.01Aug02.wnv1, W27.03Jul03.wnv1)
    • From a study in diurnal raptors, owl and corvids, it was noted that the highest rate of seroconversion (58.3%) occurred with three vaccinations, each of 1 mL (rather than lower doses), at intervals of three weeks. (J2.36.w4)
    • Vaccination resulted in no adverse reactions in any bird and varying rates of seroconversion in Spheniscus demersus - African Penguin (80% seroconversion, 16/20 birds), Eudyptula minor - Little blue penguins (5.9%, 1/17 birds), Phoenicopterus chilensis - Chilean flamingo (41%, 15/37 birds), Phoenicopterus ruber - American flamingo (Phoenicopterus (Genus)) (30%, 6/20 in one group and 60% (30/50) in another group, but none of 22 Tympanuchus cupido attwaeri - Attwater's prairie chickens (Tympanuchus cupido - Greater prairie-chicken). (J2.38.w1)
    • An apparent reaction to vaccination with the equine killed vaccine has been noted in green-naped lorikeets (Psittacidae - Parrots and allies (Family)) in Toronto Zoo, Canada, vaccinated three times in 2002 with no apparent problems, but with death of 4/18 birds 2-10 days after a single booster was given in 2003. (W27.03Jul03.wnv1); adverse reactions have also been reported for vaccinated Asio otus - Long-eared owl. (J2.38.w1)
  • Various species of birds have been vaccinated with a DNA vaccine; good immunological responses have been shown in some birds, and protection (reduced viraemia on challenge) has also been noted in Corvus ossifragus - Fish crow and Buteo jamaicensis - Red-tailed hawk. (J84.9.w15, J91.67S2.w3, J214.267.w9, P9.2004.w12, P503.1.w8)

In Israel: Commercial goose flocks in Israel have been vaccinated against WN Virus.

  • An inactivated vaccine was released for field use in Israel in 2001 and used in about 300,000 goslings in commercial flocks. (W27.06Feb02.wnv1)
    • Vaccination involves two inoculations, at two and four weeks old.
    • It has been suggested that use of this vaccination would be required for young geese being reared from before the onset of the biting insect season until cold nights decreased mosquito activity (e.g. until the end of November). (J133.951.w26)
    • Data from 2001-2003 showed that there were no outbreaks in commercial flocks (all vaccinated) over this time [2004 data]. (J70.23.w5)
  •  A turkey meningoencephalitis (TME) virus vaccine has also been used in Israel, although with some problems. (J64.19.w1, J133.951.w26)
  • The development of a live attenuated virus is ongoing. (J115.13.w2)
Associated techniques linked from Wildpro

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Vaccination of other Mammals

There has been no impetus for the development of vaccines suitable for use in mammals other than humans and horses.
  • No mammal species except humans and horses appear to be at significant risk of developing disease associated with natural WNV infection. (J64.19.w1)
    • However this situation may change with increases in reports of WNV infection causing clinical disease and mortality in other species such as reindeer (W27.16Nov02.wnv1), alpaca (W27.17Sept02.wnv1), Rocky Mountain goats and sheep (W27.20Sept02.wnv1), seals (W27.31Oct02.wnv1) and macaques (W27.24Nov02.wnv1).
  • No mammal species been identified as important amplifier or reservoir hosts for WN virus.
  • Vaccine development experiments have shown various vaccines to protect laboratory mice against WNV infection. (J80.75.w1, J115.13.w2,  J135.99.w1, J133.951.w5); both the killed virus equine vaccine (Fort Dodge) and the ChimeriVax vaccine have been shown to protect hamsters. (J84.8.w14)
  • Vaccine development experiments have shown at least one chimera vaccine to protect non-human primates against WNV infection. (W27.12Mar2002.wnv1)
  • The equine killed virus vaccine has been tested in llamas and alpacas and shown to be immunogenic in these species when given at the equine dose; following three doses, virus-neutralizing antibody levels were similar to those seen in horses after two doses of the vaccine. (J4.225.w6, W27.17Sept02.wnv1)
  • The equine killed virus vaccine has been used to vaccinate zebras and tapirs in the National Zoo, Washington DC. (W27.01Aug02.wnv1)
  • The recombinant canarypox virus encoding the prM and E genes of WN virus has been tested in dogs and cats; the vaccinated animals developed a detectable antibody response and were protected at 120 days (cats) and 135 days (dogs) against challenge infection with WNV via mosquito. (J70.23.w5)
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Authors & Referees

Authors Debra Bourne (V.w5)
Referee Suzanne I. Boardman (V.w6); Becki Lawson (V.w26); Dr Robert G. McLean (V.w42); Dr Jules Minke (V.w119)

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