Scientists 'terrified' by HK bird flu: Doherty

The risk of a SARS pandemic sweeping the world appears to be over, to the great relief of international health authorities who have been awaiting another pandemic of the magnitude of the Spanish 'flu pandemic of 1918-19, which killed an estimated 20 million people on six continents.

US Nobel laureate virologist Joshua Lederberg warned a decade ago that influenza was potentially the most dangerous virus on the planet, and the next pandemic was overdue.

During his talk on killer T-cells and viruses at the XIX International Congress of Genetics, Australian Nobel laureate immunologist Prof Peter Doherty, of Melbourne University, revealed just how worried health authorities were when a new strain of the influenza virus, the so-called 'bird flu' appeared in Hong Kong four years ago.

Doherty was describing his group's efforts to develop a new type of influenza vaccine that will induce long-lived immunity to the notoriously mutable virus, by eliciting a strongly focused cytotoxic T-cell response against highly immunogenic epitopes of selected viral proteins.

He said that when the new strain of avian influenza appeared in poultry in the Hong Kong markets, scientists were "terrified" because all efforts to grow the virus in fertilised hen's eggs failed.

For more than half a century, the standard way of producing a conventional influenza vaccine has been to grow a new strain up in large quantities, then attenuate it to produce a strain-specific vaccine.

"It was so virulent it killed the embryonated hen's eggs, so they couldn't make a vaccine," Doherty said.

Fortunately, a new molecular technique developed by renowned influenza researcher Dr Robert Webster, came to the rescue.

It involves splicing the genetic code for random segments of the new strain's surface proteins into the neuraminidase gene of a 'tame' vaccine strain of the virus -- the enzyme has a distinctive stalk-like stricture that projects from the virus' surface, which can accommodate insertions, up to a certain size, without compromising its function.

"You then have a high-growing virus for the vaccine, which is how the new influenza vaccines will be made," said Doherty.

The cut-and-splice technique will allow immunologists to experiment with various epitopes of viral proteins, to identify those that provoke the strongest cytotoxic T-cell response.

Fortunately, Doherty said, the new bird flu, which killed several people in Hong Kong, turned out to be transmissible only between birds and humans. Unlike the Spanish' flu pandemic strain, it proved to incapable of direct human-to-human transmission.