Japanese encephalitis vaccine (Ixiaro)

How does it work?

Ixiaro is a Japanese encephalitis vaccine that contains inactivated Japanese encephalitis virus. It works by stimulating the body's immune response to this virus, without causing the disease.

When the body is exposed to foreign organisms, such as bacteria and viruses, the immune system produces antibodies against them. Antibodies help the body recognise and kill the foreign organisms. They then remain in the body to help protect the body against future infections with the same organism. This is known as active immunity.

The immune system produces different antibodies for each foreign organism it encounters. This establishes a pool of antibodies that helps protect the body from various different diseases.

Vaccines contain extracts or inactivated forms of bacteria or viruses that cause disease. These altered forms of the organisms stimulate the immune system to produce antibodies against them, but don't actually cause disease themselves. The antibodies produced remain in the body so that if the organism is encountered naturally, the immune system can recognise it and attack it, thus preventing it from causing disease.

Each bacteria or virus stimulates the immune system to produce a specific type of antibody. This means that different vaccines are needed to prevent different diseases.

The Japanese encephalitis vaccine stimulates the immune system to produce antibodies against the Japanese encephalitis virus and is given to prevent this disease in people travelling to areas where the virus is a high risk.

Two doses of Ixiaro are needed, 28 days apart. This two dose course should be completed at least one week before travel to the high-risk area. It is not currently known how long this primary course provides protection against the virus for, but protection can be expected for at least one year.

The injections are usually administered into the muscle of the upper arm.

What is it used for?

  • Prevention of Japanese encephalitis in adults.

This vaccine is not given routinely. It is only given to people who are at high risk of contracting Japanese encephalitis, such as travellers to or people living or working in high risk areas.


  • This vaccine is given to prevent Japanese encephalitis only. It will not prevent encephalitis caused by other organisms.
  • People who have an underactive immune system (for example due to a genetic defect, disease such as HIV infection, or treatment with immunosuppressant medicines such as chemotherapy, high-dose corticosteroids, or immunosuppressants, eg to prevent rejection of organ transplants), may not produce enough antibodies in response to this vaccine. If you fall into one of these categories you may need to have additional doses of the vaccine to make sure you produce enough antibodies to protect you from the virus.

Not to be used in

  • Sudden feverish illness (the vaccine should be postponed until after recovery).
  • This vaccine is not recommended for children and adolescents, as its safety and effectiveness have not been studied in this age group.

This vaccine should not be used if you are allergic to one or any of its ingredients. Please inform your doctor or pharmacist if you have previously experienced such an allergy. If you feel you have experienced an allergic reaction after having this vaccine, inform your doctor or pharmacist immediately.

Use with caution in

  • Blood clotting disorders, eg haemophilia.
  • People with low numbers of blood cells called platelets in their blood (thrombocytopenia).

In both these cases an injection into a muscle could cause bleeding and, for this reason, this vaccine may be administered under the skin (subcutaneously) instead. However, the vaccine may be less effective when administered this way.

Pregnancy and breastfeeding

Certain vaccines should not be used during pregnancy or breastfeeding. However, other vaccines may be safely used in pregnancy or breastfeeding providing the benefits to the mother outweigh the risks to the unborn baby. Always inform your doctor if you are pregnant or planning a pregnancy, before having any vaccine.

  • The safety of this vaccine for use during pregnancy has not been established. It is not recommended for use in pregnancy. Seek further medical advice from your doctor.
  • It is not known if this vaccine passes into breast milk. However, since it contains inactivated virus it is not expected to be harmful to a nursing infant. Seek further medical advice from your doctor.

Side effects

Vaccines and their possible side effects can affect individual people in different ways. The following are some of the side effects that are known to be associated with this vaccine. Just because a side effect is stated here does not mean that all people having this vaccine will experience that or any side effect.

This vaccine contains no live virus and so cannot cause Japanese encephalitis.

Very common (affect more than 1 in 10 people)

  • Headache.
  • Aching muscles (myalgia).
  • Pain and tenderness at the site of injection.

Common (affect between 1 in 10 and 1 in 100 people)

  • Feeling sick (nausea).
  • Rash.
  • Fatigue.
  • Flu-like symptoms.
  • Fever.
  • Redness, hardening, swelling or itching of the skin at the injection site.

Uncommon (affect between 1 in 100 and 1 in 1000 people)

  • Diarrhoea.
  • Vomiting.
  • Sore throat.
  • Nasal inflammation, causing a blocked or runny nose.
  • Chills.
  • Bruising or bleeding at the injection site.
  • Dizziness.
  • Spinning sensation (vertigo).
  • Migraine.
  • Increased liver enzymes.

Rare (affect between 1 in 1000 and 1 in 10,000 people)

  • Inflammation of lymph glands.
  • Itching.

The side effects listed above may not include all of the side effects reported by the vaccine's manufacturer. For more information about any other possible risks associated with this vaccine, please read the information provided with the vaccine or consult your doctor or pharmacist.

How can this vaccine affect other medicines?

This vaccine is not expected to affect other medicines. However, you should always tell the doctor or nurse administering the vaccine what medicines you are currently taking, before you are given a vaccine.

If you are taking medicines that suppress the activity of the immune system, for example chemotherapy, high-dose corticosteroids, or immunosuppressants, eg used following an organ transplant, you may not produce adequate numbers of antibodies in response to this vaccine. As a result, the vaccine may be less effective. If you are taking any of these medicines you should discuss this with your doctor. You may need additional doses of the vaccine.

Other Japanese encephalitis vaccines

Unbranded Japanese encephalitis vaccines are imported into the UK on a named-patient basis.