Immunisation - Japanese Encephalitis

Japanese encephalitis can be a serious illness causing inflammation of the brain. You should consider being immunised against Japanese encephalitis before you travel to certain countries in Southeast Asia and the Far East. Check with your practice nurse at least 6-8 weeks before you travel to see if you should have this immunisation.

What is Japanese encephalitis?

Japanese encephalitis is caused by a virus. It is passed to humans by the bite of infected mosquitoes. It cannot be transmitted by other humans.

Japanese encephalitis is usually a mild illness. In many cases there are no symptoms. However, in a small number of cases (about 1 in 200 infected people) the illness is much more serious. In these people, the infection may start with fever, tiredness, headache, vomiting, and sometimes confusion and agitation. This may progress to encephalitis (inflammation of the brain). This can cause permanent brain damage and is fatal in some cases.

Japanese encephalitis occurs throughout Southeast Asia and the Far East. It is mainly a problem in rural farming areas. It occurs more commonly in the rainy season (roughly May-September) when the mosquitoes are most active.

Who should be immunised against Japanese encephalitis?

Your doctor or practice nurse can advise if you should have this immunisation for your travel destination.

Generally, it is advised for travellers who stay for a month or longer during the transmission season in rural areas of certain countries in Southeast Asia and the Far East. It may be advised for shorter trips to these countries if you are at particular high risk. For example, if you travel to areas where rice and pig farming co-exist or if you do a lot of outdoor activities.

The vaccine is also recommended for laboratory workers who may be exposed to the virus with their work.

The vaccine schedule

The vaccine stimulates your body to make antibodies against the virus. These antibodies protect you from illness should you become infected with this virus.

In May 2009, a new Japanese encephalitis vaccine, Ixiaro®, became available. This is licensed for use in adults aged 18 years and older. This is usually given as two injections; the second injection is given 28 days after the first. Full immunity takes up to a month to develop. The course of injections should be completed at least one week before departure. So, you should see your practice nurse well in advance of your travel date.

A booster dose should then be given within the second year after the initial course of two injections.

Who should not receive the Japanese encephalitis vaccine?

  • If you are ill with a fever you should postpone the injection until you are better.
  • You should not have an injection of this vaccine if you have had an allergic reaction to a previous dose of this vaccine.
  • There is no evidence of risk with this vaccine if you are pregnant or breast-feeding. However, if you are pregnant or breast-feeding, it is usually only given if the risk of Japanese encephalitis is very high and cannot be avoided.
  • Children should not receive this vaccine. Children aged over 1 can have an alternative vaccine - the Green Cross® (GC) Japanese encephalitis vaccine. However, Japanese encephalitis GC vaccine is not licensed in this country at present and is supplied on a named patient basis.
  • The GC vaccine may be given with more caution if you have a previous history of allergy to bee or wasp stings or have asthma or allergic rhinitis.

Are there any possible side-effects from the vaccine?

  • Mild pain and redness occur at the site of injection in some people.
  • The most common side-effects after receiving the Ixiaro® vaccine are headache and muscle aches.
  • Other less common reactions with the Ixiaro® vaccine include a flu-like illness, fever and fatigue.
  • Reactions such as fever, muscle aches and vomiting are more common after the GC vaccine.

You should also try to prevent mosquito bites

Immunisation is only one aspect of preventing illness whilst abroad. Immunisation is not 100% effective and you should also try to avoid mosquito bites when in 'at-risk' areas.

Mosquito bites can be avoided by the following:

  • Sleep in rooms that are properly screened. For example, rooms with close-fitting gauze over windows and doors.
  • Spray the bedroom with insecticide just before evening. This kills mosquitoes that may have come into the room during the day.
  • If you sleep outdoors or in an unscreened room, use mosquito nets impregnated with an insecticide (such as permethrin). The net should be long enough to fall to the floor all round your bed and be tucked under the mattress. Check the net regularly for holes. Impregnate with fresh insecticide every six months.
  • Use an electric mat to vaporise insecticide overnight. Burning a mosquito coil is an alternative.
  • Mosquitoes that carry the Japanese encephalitis virus are most active at dusk and in the evening. If possible, avoid going out after sunset. If you do go out after sunset then wear long-sleeved clothing, trousers, and socks. Light colours are better, as they are less attractive to mosquitoes.
  • Apply insect repellent to clothing or exposed skin. Diethyltoluamide (DEET) is safe and effective, but take advice on the best repellent in the area you visit.

Further information

Information on immunisation from the NHS


Department of Health

See the Health Advice for Travellers leaflet.
All travellers going abroad are advised to get this booklet. You can get a free copy from main post offices.

The National Travel Health Network and Centre (NaTHNaC)


Has links to UK websites on travel health -