Professor Brendan Murphy made the comment while explaining why Australia has banned arrivals from virus-hit Iran, but not two other major hotspots, Italy and South Korea.

"It is no longer possible to absolutely prevent new cases coming in, given the increasing changes in epidemiology around the country," Prof Murphy told reporters on Monday.

He said the Iran outbreak was considered high risk, and the travel ban was considered an effective strategy to slow the spread of the disease.

But a different view has been taken on Italy and South Korea, where outbreaks are considered contained, confined and localised.

"In the case of Iran, it's such a high risk that a travel ban is worth doing because it will slow down the number of cases," Prof Murphy said.

"In Italy and South Korea, where they have large outbreaks but they are confined and (have) been localised, the risk, the proportionality of putting in a travel ban was not justified in terms of its benefits to the health protection of the Australian community."

The government has upgraded its travel advice for Italy.

Australians intending to travel there have been told to exercise a high degree of caution across the entire country, and to reconsider the need to travel to 10 virus affected towns in Italy's north.

Federal Health Minister Greg Hunt also said any health and aged-care workers returning from Italy and South Korea must not go to work for two weeks because they could infect vulnerable populations at greatest risk of dying.

"As a healthcare worker, or as a residential aged care worker, you should not attend your regular work for 14 days," Mr Hunt said.

"That is an additional level of protection which has been advised by the chief health and medical officers and accepted by the Australian government."

Australian Associated Press