Japanese encephalitis virus (JEV) information for health professionals

Japanese encephalitis

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.


As part of the national response to the Japanese encephalitis virus (JEV) outbreak, SA Health is offering free  Japanese encephalitis virus (JEV) vaccines to groups identified for priority vaccination by the Communicable Diseases Network Australia (CDNA), as well as other vulnerable members of the community.

Vaccines will be distributed to existing Vaccine Distribution Centre providers who have agreed to provide JEV vaccines via the current vaccine distribution pathways. Detailed plans for the delivery of vaccinations will be developed in conjunction with the relevant Local Health Networks, general practitioners and pharmacists.

Eligibility criteria

The initial priority group identified by the CDNA includes people who work at, reside at, or have a planned non-deferable visit to a:

  • piggery, including but not limited to farm workers and their families (including children aged 2 months and older) living at the piggery, transport workers, veterinarians and others involved in the care of pigs
  • pork abattoir or pork rendering plant
  • personnel who work directly with mosquitoes through their surveillance (field or laboratory based) or control and management, and indirectly through management of vertebrate mosquito-borne disease surveillance systems (e.g. sentinel animals) such as:
    • environmental health officers and workers (urban and remote)
    • entomologists
    • all diagnostic and research laboratory workers who may be exposed to the virus, such as persons working with JEV cultures or mosquitoes with the potential to transmit JEV; as per the Australian Immunisation Handbook.

SA Health has expanded the eligibility criteria to reduce risk to the communities with a high risk of exposure to JEV from infected mosquitos.

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


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

Imojev is a ‘live’ attenuated vaccine, which means it contains a weakened version of the live virus JEV.  Imojev is the recommended vaccine for the 2022/23 JEV Immunisation Program.

  • 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 has been 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 to be entered onto the AIR/practice software as Ixiaro.

Anyone aged <5 years or who requires the JEspect will be referred to their GP or the immunisation clinics held by the Alexandrina Council.

Pharmacies will only be administering Imojev and vaccinating people >5 years of age.

Co-administration with other vaccines

ATAGI advises that either Imojev or JEspect can be co-administered with other vaccines if required. For more information see the Australian Immunisation Handbook1.


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

Variation from product information

The Australian Product Information for JEspect currently states that this vaccine is for use in people aged ≥18 years. ATAGI recommends that children and adolescents aged ≥2 months to <18 years can receive this vaccine. This is based on paediatric studies.10-12 It should also be noted that numerous other regions and countries (e.g. the USA, UK, Europe) have registered and recommended the use of JESpect from 2 months of age. 20-22

Recommended dosages (health.gov.au /health-alerts/japanese-encephalitis-virus-jev/clinical-guidance)

Vaccine Age group Dose Contraindications
Imojev ≥9 months Single dose schedule 0.5 mL subcutaneously (SC) Pregnancy immunocompromised (live attenuated vaccine). Recent receipt of immunoglobulin or immunoglobulin containing blood products (within last 6-12 weeks). Anaphylaxis to vaccine or component
JEspect 2 months to <3 years 2-dose schedule 0.25 mL IM 28 days apart Anaphylaxis to vaccine or component, including a serious hypersensitivity reaction to protamine sulphate (for JEspect only)
≥3 years 2-dose schedule 0.5 mL IM 28 days apart (7 days apart for adults aged ≥18 years if imminent exposure) None

JEV online learning resource

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


The normal lifecycle of JE virus is between waterbirds and mosquitoes, which may then transfer over to pigs and horses. 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.


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.


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.


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 Immunisation Section on 1300 2332 272 (Monday to Friday between 9.00 am and 5.00 pm).

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 Fight the Bite
  • 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.