This follows the Government's announcement that children who travel to countries where swine flu is widespread will be banned from attending school for a week on their return.

Robert Booy, the head of research at Westmead's National Centre for Immunisation Research and Surveillance, said children were ``super spreaders''.

``Their immune systems are not strong enough to get over the virus quickly ... the first time they get it, they could be infectious for 10-14 days whereas adults would get over in less than a week.''

Scientists in Australia, the US and Europe are working on a vaccine for the H1N1 swine flu virus and it is likely to be available in August.

Children under five and health professionals would be given priority as they were deemed most at risk of infection, Professor Booy said.

As of May 25, there were 17 confirmed cases in Australia, including 2 in NSW.

Professor Booy said the virus was spreading slower than originally thought here and the current strain had caused only mild symptoms so far.

But ``we do need to keep an eye on it as it could change to the point where it is more novel and particularly more nasty''.

The vaccine would cover all strains, he said.