Flooded inland areas have caused mosquito numbers to explode heading into what is expected to be another dangerous summer.

The killer virus has already been found to have survived the winter along the Murray River with more infected pigs already found as part of surveillance measures.

"Despite the winter season where mosquito populations usually diminish, it appears the Japanese encephalitis virus has continued to circulate along the Murray River, presumably between mosquitoes and waterbirds," NSW Health executive director Dr Jeremy McAnulty said.

JEV has been responsible for the deaths of at least seven people around Australia since the surprise outbreak earlier in the year.

There have been 39 human cases in Australia including - NSW 13, Queensland 2, South Australia 5 and Victoria 9.

The plans of several states to offer free vaccines to a growing number of local government areas to prevent more fatalities is heading to a COVID-19 style shortage of vaccines.

Victoria and NSW say they are able to meet most demand for vaccines from an existing stockpile which is running out.

"Supply of JEV vaccine continues to be severely constrained in Australia," NSW Health says.

"People who are eligible for vaccination are urged to come forward for vaccination with stock currently available in NSW, and additional vaccines are expected to arrive in the first part of 2023."

"There is significant global demand for the JEV vaccine," Victoria's Health Department says.

"Victoria has a limited supply and therefore access is restricted to specific priority groups, targeted to those most at risk. Eligibility criteria will continue to be monitored."

IN OTHER NEWS:

Available stocks of vaccines are prioritised for people aged two months or old who live or routinely work in the following council or town areas:

NSW: Albury, Balranald, Berrigan, Bland, Bogan, Bourke, Brewarrina, Broken Hill, Carrathool, Central Darling, Cobar, Coolamon, Coonamble, Dubbo Regional, Edward River, Federation, Forbes, Gilgandra, Goulburn Mulwaree, Greater Hume, Griffith, Hay, Junee, Lachlan, Leeton, Lockhart, Moree Plains, Murray River, Murrumbidgee, Narrabri, Narrandera, Narromine, Parkes, Temora, Unincorporated Far West Area, Wagga Wagga, Walgett, Warren, Warrumbungle, Weddin and Wentworth.

Victoria: Campaspe, Gannawarra, Greater Shepparton, Indigo, Loddon, Mildura, Moira, Swan Hill, Wodonga, Towong, Benalla, Wangaratta and Strathbogie.

In Queensland free vaccines are available in Balonne, Goondiwindi, North Burnett, Quilpie, South Burnett, Western Downs or southwest area of Toowoomba Regional Council (surrounding and including Millmerran) and people who live or work in the Torres Strait and/or Northern Peninsula Area of Cape York.

South Australia has joined the free program vaccine program for Swan Reach, Blanchetown, Goolwa, Mannum, Murray Bridge, Milang, Lake Alexandrina, Raukkan, Tailem Bend, Meningie, Morgan, Cadell, Qualco, Waikerie, Kingston-on-Murray, Moorook, Loxton, Paringa, Renmark, Monash, Berri, Gerard, Glossop, Barmera, Cobdogla, Cambrai.

The criteria also specifies they must:

There are two JEV vaccines offered in Australia:

With the pressure on vaccines, health authorities in all states are continuing to roll out the message to prevent mosquito bites including applying repellent regularly to all areas of exposed skin, wearing loose, long-sleeved, light-coloured clothing and covered footwear when outside, and mosquito proofing homes.

The latest data from mosquito monitoring programs in NSW shows "very high" numbers of mosquitoes in the Murray River region, however the species of mosquito most capable of spreading JEV, Culex annulirostris, were detected in low numbers.