The South Australian government must urgently source more stocks of the Japanese encephalitis vaccine and expand the criteria for those eligible for the jabs, the state opposition says.

The opposition says concerns are growing about the potentially deadly virus and its spread through SA.

Tests from trapped mosquitoes have also revealed much higher numbers carrying the Ross River and Barmah Forest viruses this summer.

Opposition leader David Speirs says despite the increased risk, the eligibility criteria for the free JEV vaccine remains tight with it being provided only to those who live or work in certain flood-affected areas and who also spend at least four hours outside each day.

"JEV can cause permanent brain damage and even death and now we're seeing health alerts quietly pop up at reservoirs to warn people of the threat of virus-carrying mosquitoes," Mr Speirs said.

"It's clear JEV is no longer a Riverland-specific problem."

Mr Speirs said Premier Peter Malinauskas should source more vaccine supplies.

"Peter Malinauskas needs to up his game and communicate concisely with South Australians about the virus so they don't unknowingly put their health at risk," he said.

"There shouldn't be any hurdles in place for those who wish to protect themselves ahead of travelling to our river communities and now those living in the metropolitan area."

In recent public warnings, Chief Public Health Officer Nicola Spurrier said the best protection from mosquito-borne viruses was to not get bitten.

"We have an explosion in mosquito populations at the moment, so it is vital that South Australians protect themselves," she said.

"Remain vigilant, wear long-sleeved and light-coloured clothes and apply an insect repellent if you are outside."

SA Health said the supply of JEV vaccines was limited in Australia.

It said the eligible groups might be expanded once more vaccine was available.