Long post alert!
TheyDressedMeUpLikeThis - WHO walk a tightrope when it comes to international travel advice. They can't make any country do anything and they can't force any country to cooperate. The only weapon they have is diplomacy.
During the SARS pandemic in 2003 WHO did advise travellers to 'consider postponing all but essential travel' (not quite the same thing as advising travel restrictions) to some areas, starting with Guangdong Province in China and Hong Kong on April 2nd, almost a month after they issued a global alert. They never issued this travel advice for China as a whole or any other country as a whole.
At the time, China was not putting in place any containment measures and was not sharing much information with WHO at all. China did not even permit WHO to go to Guangdong until April 2nd and it was not until after this permission was granted that WHO issued their first travel advice for the region. It took until late April for mainland China to start shutting down restaurants, bars and clubs.
After SARS, WHO received lots of praise for how they had handled the pandemic but countries were worried that in future disease outbreaks they might themselves be the subject of travel advisories, which of course have a major impact on economies.
In 2005 they updated the International Health Regulations - a legally binding (but unenforceable) international law which states what member countries and WHO must do to prevent and respond to to the international spread of disease.
The purpose and scope of these Regulations are to prevent, protect against, control and provide a public health response to the international spread of disease in ways that are commensurate with and restricted to public health risks, and which avoid unnecessary interference with international traffic and trade.
www.who.int/ihr/publications/9789241580496/en/
Article 17 of the IHR says:
When issuing, modifying or terminating temporary or standing recommendations, the DirectorGeneral shall consider:
...
(d) health measures that, on the basis of a risk assessment appropriate to the circumstances, are not more restrictive of international traffic and trade and are not more intrusive to persons than reasonably available alternatives that would achieve the appropriate level of health protection;
Article 43 says that member states can independently implement additional health measures, however:
Such measures shall not be more restrictive of international traffic and not more invasive or intrusive to persons than reasonably available alternatives that would achieve the appropriate level of health protection
and ...
3. A State Party implementing additional health measures referred to in paragraph 1 of this Article which significantly interfere with international traffic shall provide to WHO the public health rationale and relevant scientific information for it. WHO shall share this information with other States Parties and shall share information regarding the health measures implemented. For the purpose of this Article, significant interference generally means refusal of entry or departure of international travellers, baggage, cargo, containers, conveyances, goods, and the like, or their delay, for more than 24 hours.
Further paragraphs say WHO must assess the provided rationale and supporting evidence and if not satisfied they 'may request that the State Party concerned reconsider the application of the measures.'
So this international law, agreed upon by all WHO member states, is very clear that restricting travel should be a last resort when no less restrictive alternatives are available and should be based solely on a public health rationale, backed up by scientific evidence. It's not something you do at the first opportunity, just in case.
If countries fear restrictive travel advisories they are less likely to report outbreaks of disease. If travel advisories are issued without a solid, evidence based, public health rationale then countries are less likely to cooperate and WHO can't make them.
Coming back to the current covid outbreak, Hubei was quarantined on January 24th and by the end of January pretty much the entire country was already on lockdown and anyone travelling in or out of China had to fill in a health declaration and provide their details so they could be traced.
On January 24th, when there were 11 cases outside China, WHO advised all countries to start temperature screening international travellers on entry and also on exit from countries with ongoing community transmission (just China at the time).
www.who.int/news-room/articles-detail/updated-who-advice-for-international-traffic-in-relation-to-the-outbreak-of-the-novel-coronavirus-2019-ncov-24-jan
By February 1st, when Australia banned travel from China, there were already cases in 23 countries outside of China. Unlike China, these countries were not in lockdown and most had no detection or containment measures in place, including exit screening at airports.
So while a travel ban on China might have seemed like the obvious thing to do, it doesn't make much sense because that horse had already bolted. The main threat was no longer coming from China because they were already under severe restrictions. The threat was from the 23 other countries. It's difficult to see any public health benefit from Australia's travel ban and as such it's not consistent with the International Health Regulations.
Australia has certainly managed to contain this virus better than many countries but it would be better to look at the entire package of measures they have introduced in order to find out why.
After all, the US also introduced a travel ban on China from January 31st. That's going well.