Japanese encephalitis virus (JEV) information for health professionals

Japanese encephalitis (JE) virus is spread to humans through mosquito bites. Most people do not experience any illness, but it can cause a rare and potentially life-threatening infection of the brain.

Vaccination

SA Health is offering free Japanese encephalitis virus (JEV) vaccines to selected groups.

For information on all eligible groups including proof of eligibility required please see the Japanese encephalitis virus (JEV) vaccine page.

Vaccines

There are two JEV vaccines available in Australia – Imojev and JEspect.

Imojev is the only vaccine available through the SA Health funded JEV Vaccination Program.

Imojev is a ‘live’ attenuated vaccine, which means it contains a weakened version of the live virus JEV.

• Imojev can be given to people from 9 months of age (dosage is 0.5 mL given by subcutaneous injection)
• Imojev is contraindicated in pregnant women, or people who are immunocompromised. It is not recommended for women who are breastfeeding
• People should avoid getting pregnant for 4 weeks (28 days) after having the Imojev vaccine
• You cannot receive Imojev if you have had a product containing immunoglobulin in the preceding 3 months
• Only one dose of Imojev is needed.

JEspect is an inactivated vaccine and is available to those who cannot have the live vaccine.

• This includes infants from 2 months to less than 9 months of age, people who are immunocompromised and women who are pregnant or breastfeeding
• JEspect vaccine requires two doses given 28 days apart
• If the person is at risk of immediate exposure, the 2 doses of the vaccine can be given 7 days apart if aged ≥18 years
• Children from 2 months to less than 3 years of age receive a lower dose (0.25 mL), which is half the dose given to people from 3 years of age (0.5 mL)
• Note: Some JEspect was supplied by Seqirus with the trade name Ixiaro. ATAGI have advised JEspect is also known as Ixiaro in some other countries (manufactured by Valneva and distributed in Australia by Seqirus/CSL).
• Ixiaro is entered onto the AIR/practice software as Ixiaro.

Booster dose recommendations

As per the Australian Immunisation Handbook, JEV Booster doses are recommended 1–2 years after the primary dose for those with ongoing risk of JEV exposure for:

• children aged less than 18 years at the time of vaccination who received Imojev or JEspect, and
• adults aged 18 years or older at the time of vaccination who received JEspect vaccine.

Booster doses are funded as part of the South Australian JEV vaccination program for people who meet the eligibility criteria.

As per the Australian Immunisation Handbook, Imojev can be used as a booster dose in people who received JEspect for their primary course if the live vaccine is not contraindicated.

Please note: People aged 18 years or older at time of vaccination who were vaccinated with Imojev do not require a booster dose.

For more information on booster dose recommendations, refer to the Table: Recommended doses of Japanese encephalitis vaccines and the JEV chapter in the Australian Immunisation Handbook.

Co-administration with other vaccines

ATAGI recommends Imojev can be co-administered with any other vaccine if required. Recommended intervals between live vaccines apply for vaccines not given on the same day.

For information on co-administration with other vaccines refer to the Australian Immunisation Handbook.

Adverse event following immunisation (AEFI)

It is mandatory for medical practitioners, and independent immunisers to report notifiable adverse events following immunisation (AEFI) in South Australia.

For more information on reporting an AEFI see the Adverse Event following immunisation page.

Recommended dosages

JEV online learning resource

A JEV learning resource for health professionals is available online through the NCIRS website.

Transmission

The normal lifecycle of JE virus is between waterbirds and mosquitoes, which may then transfer over to pigs, horses and other mammals. Animals and people become infected through the bite of infected mosquitoes.

Mosquitoes involved in the transmission of JE virus are primarily Culex species. The specific species of mosquito implicated in Australia is not yet confirmed.

There is no evidence of transmission from person to person. It cannot be contracted through eating meat products.

Symptoms

Over 90% of JEV infections are asymptomatic.

Acute encephalitis is a serious manifestation and occurs in less than 1% of cases of JEV infection. This is characterised by:

• headache
• fever
• seizures (usually generalised tonic-clonic)
• focal neurological signs, and
• depressed level of consciousness.

Acute encephalitis has a high case-fatality rate of around 30%. There is no specific treatment. Approximately half of those who survive the acute illness will have neurological sequelae.

JEV infection may also manifest as a milder undifferentiated febrile illness. It sometimes also presents as acute flaccid paralysis or aseptic meningitis.

Information for patients about signs and symptoms can be found on the Japanese encephalitis - including symptoms, treatment and prevention page.

Testing

Test for flaviviruses including JEV in persons with suspected encephalitis/meningoencephalitis without identified cause. Send the following: 

• Serum (2 mL in children, 5-8 mL in adults) including both acute and convalescent specimens (3-4 weeks post onset) for serology for flaviviruses including JEV
• Blood for PCR and culture for flaviviruses including JEV
• CSF (at least 1 mL) for PCR, culture, and serology for flaviviruses including JEV
• Urine for PCR and culture for flaviviruses including JEV.

Routine testing for serology is not recommended prior to vaccination.

Notification

Japanese encephalitis is an urgent notifiable condition that must be notified immediately to SA Health if suspected or confirmed by medical practitioners and pathology services by phoning the Communicable Disease Control Branch on 1300 232 272.

Treatment for Japanese encephalitis virus

There is no specific treatment for infection with Japanese encephalitis virus. Serious illness with encephalitis requires management in hospital.

Prevention of Japanese encephalitis virus

• Immunisation against JEV will not protect people from other mosquito borne diseases.
• People should take steps to limit their exposure to mosquitoes. There are simple steps people can take to protect themselves against mosquito-borne diseases. For more information, see Mozzies suck.
• Exclusion from childcare, preschool, school or work is not necessary.
• All people who work with potentially infected animals or work in areas in which infected mosquitos may be present should wear appropriate personal protective equipment (PPE). The PPE should be chosen based on the assessed level of risk and the task.