Japanese encephalitis: What it’s worthwhile to learn about vaccines for the mosquito-borne virus

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For a long time, vaccination against the Japanese encephalitis virus has mostly only been available through travel doctors, for people heading overseas.

But now that cases have been detected in southern parts of Australia for the first time, the federal government is expanding its vaccination program.

For most people, the virus will be mild. About 99 per cent of people who get infected will have very mild or no symptoms. But for the small number who do develop severe encephalitis – an inflammation of the brain – it can be deadly.

So should you consider getting vaccinated against this virus, and what vaccines are available?

Who can get the vaccine?

Before the recent cases in southern Australia, the vaccine was mostly recommended for people traveling to Asia or the Torres Strait.

People who worked with animals could also choose to get vaccinated, but it wasn’t cheap.

JEV can be spread by some types of mosquito.(Pixabay)

Now the federal government is targeting priority, “high risk” groups, including:

  • workers at piggeries, pork abattoirs, or pork-processing plants
  • people who live at or need to visit one of those locations
  • workers who deal directly or indirectly with mosquitoes
  • laboratory workers who may be exposed to the virus.

The vaccine will be free for those groups, and the government is also purchasing 130,000 JEV vaccines — additional to the 15,000 already in Australia — that will be available from late March into April.

Should I get vaccinated for the virus if I’m not in a ‘high-risk’ group?

There is no recommendation for the general population to get vaccinated against this virus.

However Associate Professor Lara Herrero, a virology research leader at Griffith University, said it was important to monitor the virus’s spread in case the priority groups needed to change.

What is Japanese encephalitis virus/JEV?

  • JEV is a virus carried by some types of mosquitoes
  • Mosquitoes can only pass it to humans by biting them
  • It’s mostly found in parts of Asia and the Torres Strait
  • Less than 1pc of cases will develop severe disease

“It’s probably too early to make a blanket statement of whether or not the whole population should be vaccinated,” Dr Herrero said.

“At this point, I think the correct strategy would be to go with high risk groups and then as the situation evolves, we would reassess and make the required recommendations.”

Infectious diseases physician Paul Griffin said he did not think the general population needed to consider getting vaccinated yet, because for most people the risk was very small.

“If we start to see cases outside of those very high-risk settings, then perhaps our vaccination rollout might expand to those areas, but that’s actually pretty unlikely,” he said.

“It’s not something that people in the general community need to be worried about right now.”

What vaccines are available for Japanese encephalitis virus, and which vaccine is best?

The two JEV vaccines available in Australia are Imojev (Sanofi-Aventis Australia) and JEspect (Seqirus).

Imojev is a single-dose, live-attenuated vaccine — which means it contains a weakened version of the virus.

A box showing Imoojev vaccine with a syringe in the foreground. Imojev is one of two JEV vaccines available in Australia.(supplies)

Dr Herrero said its advantages included being “highly efficacious” and offering about five years of protection.

On the flip side, it’s not suitable for pregnant women or people who are immunocompromised.

It also has to be kept cold, which can make storing and transporting it tricky.

JEspect only offers full protection after two doses, but is suitable for most people who cannot receive the Imojev vaccine.

It is an inactivated vaccine, which means it is more stable at room temperature and easier to store and maintain.

Dr Herrero said after two doses it offered about two years of protection, but a third dose could bring that up to six years.

As for which one you should get, Dr Herrero says there’s no simple answer.

“It depends on factors such as your personal medical history, as well as what’s actually available in the clinics near you because this is not a vaccine that is, as of yet, that widely available,” she said.

“Previously it’s only been for travelers and high-risk populations of which now is a changing definition.”

Like most medical advice, the best thing to do is speak to a doctor.

How should I prevent Japanese encephalitis virus if I cannot get a vaccine?

There have been no cases of human-to-human transmission, and you cannot get JEV from eating pork products, so you don’t have to worry about getting infected from your friends or food.

You can only catch JEV from mosquitoes, so the best way to avoid it is to avoid being begging.

Some tips to avoid mozzie bites are:

  • use a good insect repellent on exposed skin
  • wear long-sleeved clothing
  • prevent them getting into your home with fly screens.

Mosquitoes breed in stagnant water, so if you can prevent this around your home that helps reduce their numbers. Removing anything from your yard that can collect water, changing your pet’s drinking water regularly, and cleaning drains so they run freely can all help.

A single-storey white house with a neat yard, with a sky setting in the background. One way to protect yourself is by preventing mosquito breeding habitat around your own home.(Unsplash: Gus Ruballo)

Dr Herrero said mosquitoes generally don’t fly long distances, so reducing the risk in your immediate environment was one of the best ways to protect yourself.

“I would say to [people in the general population] I would be doing all I can to prevent mosquito breeding habitats in my backyard, and I would be doing all I can to prevent being asked myself,” she said.

Read more about Japanese encephalitis:

Mosquitoes get infected by biting an infected animal, such as a pig, and then can only pass it onto humans by biting them. But even if you’re far away from a piggery or considered low risk, it’s a good idea to avoid getting bitten anyway.

“We’re lucky to already have two very safe and effective vaccines, that can be rolled out to those people that require them, but the number of people that are going to require it in our country is likely to be very small,” Dr Griffin said.

“The main thing is to make sure you take steps to avoid getting bitten by mosquitoes.”

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