This is a transcript from PM. The program is broadcast around Australia at 5:10pm on Radio National and 6:10pm on ABC Local Radio.

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MARK COLVIN: A worrying new research paper has been published in the United States.

It proves that H5N1 bird flu, which has so far only killed people in its pure form is capable of combining with conventional human flu viruses.

A mutated virus combining human flu and bird flu is the nightmare strain which scientists fear could create a worldwide pandemic.

The research was conducted in a laboratory by the US Centers for Disease Control.

Jeff Waters reports.

JEFF WATERS: The great bird flu pandemic of 1918 was caused by an avian influenza virus which spread from birds and then directly from human to human. And it's a pure bird flu strain called H5N1 which has caused hundreds of deaths recently around the world.

But there were also pandemics in 1957 and '68 which were caused when a bird flu combined with a human form of influenza and then spread globally.

Now scientists at the Centers for Disease Control in the United States have proven that the very deadly H5N1 virus can also mix with human flu. It's only happened in the laboratory but it's causing concern.

Dr David Smith is a director if microbiology and infectious diseases at PathWest laboratories in Perth.

DAVID SMITH: It increases the level of concern that we may get a bad pandemic. It doesn't change our ongoing uncertainty about whether and when the pandemic will occur. That's something that is controlled by events that occur in nature and they are chance events that we can't accurately predict.

JEFF WATERS: What the new research doesn't tell us is whether this new variety of mixed virus could spread easily. But Dr David Smith says it does further our understanding of what may happen.

DAVID SMITH: I think it's important information for us to understand how pandemic strains may emerge and how bad they may be. Of course this was, if you like, deliberately created in a safe laboratory setting in order to show what might happen.

However, in actual human populations, there are a lot of other things that can happen in terms of how the viruses might mix and what might results from it. So it really tells us a potential, it doesn't tell us what is going to occur and that's unfortunately the problem with predicting human pandemics.

JEFF WATERS: The report has emerged at the same time as other worrying news. The Indonesian Government has announced it will stop reporting bird flu deaths as they happen, reportedly because it doesn't want bad news to spread.

Indonesia has suffered the greatest number of H5N1 deaths. Jakarta has admitted that a teenager died of the disease last month, but it only reported details of the incident this week.

Professor Anne Kelso from the World Health Organisation Collaborating Centre in Melbourne says such a move would hinder efforts to contain any outbreak.

ANNE KELSO: The sharing of information and the sharing of viruses are the two most important things that countries can do to help the world prepare for a potential pandemic. So this is, if it turns out to be true, it's a worrying step on behalf of the Indonesian Government to no longer share information about deaths as they happen.

We don't need to know who the people are. It's very important we know where the deaths are occurring and if possible to have access to the viruses to compare with other viruses from around the world.

JEFF WATERS: What could happen if the Indonesians did do this and didn't report these deaths?

ANNE KELSO: It simply means that we have less warning as a world. The WHO on behalf of all the member states will have less warning if there are changes happening that could lead to a pandemic.

In particular it's important to know whether the deaths are due to exposure to viruses in poultry or whether there's evidence that they are being transmitted from human to human.

MARK COLVIN: Professor Anne Kelso from the World Health Organisation Collaborating Centre in Melbourne, talking to Jeff Waters.