Containment disruptive but necessary: PM

The federal government's decision to move to a containment stage to deal with swine flu will be disruptive but necessary, Prime Minister Kevin Rudd says.

Mr Rudd said he had been briefed by Australia's chief medical officer and there had been 13 confirmed cases of the virus in Australia to date.

"The government has acted in response to each and every recommendation put to the government by the professional health authorities across our nation," he told reporters in Sydney on Saturday.

"This will of course involve inconvenience to communities as certain schools are temporarily closed down."

Mr Rudd said he understood that would cause inconvenience to families.

"However, we also have the responsibility for the public health of the nation and therefore we will take whatever actions are necessary to underpin the public health of the nation," he said.

Earlier, Health Minister Nicola Roxon said new cases should now be expected with every hour, in keeping with expert predictions the virus would eventually side-step border control efforts and spread within the community.

"We were never going to dodge that bullet," says Professor Robert Booy, Head of Clinical Research at the National Centre for Immunisation Research & Surveillance, at the University of Sydney.

"Given two billion commercial air travellers a year it was always going to come to Australia within about a month.

"This is a virus that is clearly transmitting human-to-human in other countries and now it is expected to do that in Australia."

Professor Bill Rawlinson, from the Department of Virology at Sydney's Prince of Wales Hospital adds: "In a public health sense ... we now think that swine flu is here."

Confirmed H1N1 cases increased to 12 on Friday, with two of these considered the first person-to-person transmissions on Australian soil.

A 17-year-old boy from Melbourne's northern suburbs and a 15-year-old Adelaide girl had no traceable contact with any of the existing swine flu carriers, or contact with recent international travellers.

The girl's school has been closed for a week, and Prof Booy says containment efforts and a community-wide personal hygiene crackdown would dictate how quickly the virus would spread.

The experience from overseas was an average rate of 1.5 new infections for every existing case, every two to three days.

"Over the next few months the number of people affected will rise dramatically," Prof Booy says.

"You'd be hesitant to shake hands with people at the moment but you can still smile at them.

"And if people have got classical symptoms such as fever plus any respiratory symptoms - especially a cough or a runny nose - then you shouldn't come to work."

Efforts to make a matched vaccine were continuing but it would not be available until the end of August, at the earliest.

Adults and older people were thought to be naturally more resistant to swine flu which has tended to infect more children and teens.

The virus' spread across the world had also revealed it was not as deadly as initially feared, Prof Booy says, but while it behaved very similarly to "standard garden-variety influenza" it should not be underestimated.

Prof Booy says about 2,500 Australians die annually from ordinary seasonal flu and swine flu could "double the annual death rate, so it's not trivial".

People most at risk are those over 75, the very young, pregnant women, those with a compromised immune system or other illness such as heart, lung or kidney disease.

The majority of people, Prof Booy says, were likely to feel "unwell for some days but they'll recover" from swine flu.

"If you contract it your chance of dying is less than one in a thousand, however, given its novelty its likely that a higher proportion of the population will be affected," he says.

Professor Raina MacIntyre, who is Head of the School of Public Health and Community Medicine at the University of NSW, sits on the Scientific Influenza Advisory Group to the Chief Medical Officers of Australia.

She says up to 40 per cent of the population could become infected during a swine flu pandemic - eight million Australians.

"But with our best mitigation efforts we might drop that down to ten per cent of the population, so two million," Prof MacIntyre says.

"Once we know that there is sustained community transmission ... the focus shifts from keeping the infection out to controlling it as much as possible within the community."