Japanese Encephalitis Immunisation

What is Japanese encephalitis?

Japanese encephalitis is caused by a virus. It is passed to humans by the bite of infected mosquitoes. It can not 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 South East 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 South East 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 coexist or if you do a lot of outdoor activities.

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

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. Note: the Japanese encephalitis vaccine is not licensed in the UK. Therefore, it must be given on a named patient basis.

The usual schedule is three injections of this vaccine. The second dose is given seven days after the first. The third dose 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 two weeks before departure. So, you should see your practice nurse well in advance of your travel date. Children between one and three years should receive half the adult dose.

(An alternative is to have two injections of vaccine, one week apart. This gives less immunity though.)

You should have a booster dose after one year and then every three years if you remain in, or return to, an 'at risk' area.

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 breastfeeding. However, if you are pregnant or breastfeeding it is usually only given if the risk of Japanese encephalitis is very high and cannot be avoided.
• The 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.
• Children under one year should not receive this vaccine.

Are there any possible side-effects from the vaccine?

• Mild pain and redness occur at the site of injection in some people.
• An allergic reaction occurs in a small number of cases. This can cause a rash, swelling of the face, and, rarely, breathing problems. The allergic reaction can occur within minutes of having the injection, but can be delayed for up to two weeks. Therefore, the course of injections should be completed at least 10 days before your travel departure - just in case you have a reaction which may need treatment. If you experience any of these symptoms you should see your doctor without delay.

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

Health Advice for Travellers.

All travellers going abroad are advised to get this booklet by the Department of Health. You can get a free copy from main post offices.

The National Travel Health Network and Centre (NaTHNaC)

Web: www.nathnac.org

Patient UK Travel Health Page

Web: www.patient.co.uk/showdoc/38/
Has a comprehensive list of links to UK websites on travel health.