Roche AG’s Tamiflu anti-influenza drug has been proven to work against H5N1, the strain of the avian flu virus that the World Health Organization says could be the source of a deadly flu pandemic.

In a study released late on Sunday, researchers from the Queen Mary Hospital in London said that oseltamivir, marketed by Roche as Tamiflu, is effective against avian and human forms of the virus, which has so far killed 32 people this year. Tamiflu belongs to a drug class known as neuraminidase inhibitors, which block the action of viral enzymes.

“Since the influenza virus is constantly mutating, today’s is the first data to show oseltamivir to be effective against this highly pathogenic strain, which is currently circulating in Vietnam and Thailand,” the researchers said in a study.

The WHO had already singled out Tamiflu as its drug of choice to protect against bird flu and in case of a human flu pandemic. It was previously proven effective in managing an outbreak of the H7N7 avian strain in the Netherlands in 2003, which infected around 1,000 people, the researchers said.

Roche certificates were last trading 0.3 percent higher at 122.70 Swiss francs in a slightly firmer Swiss market.

Tamiflu, Roche’s 12th-biggest drug last year with 431 million Swiss francs ($359.2 million) in sales, is approved in the United States, Japan and Europe as a treatment for type A and B influenza, and Roche had said in January that it might work against H5N1.

The latest study, to be presented at a conference on Antimicrobial Agents and Chemotherapy in Washington D.C. this week, said a total of 44 cases of human infection, 32 of which were fatal, had been detected since the start of the year.

The WHO said on Sunday the world was overdue a pandemic that could kill millions and that the H5N1 virus now killing tens of millions of birds in Asia was the most likely source.

Flu pandemics - global epidemics of new strains of disease that kill a usually higher number of people - come on average every 27 years. The last one was in 1968.

“These new data and the experience in the Netherlands add to previous studies by the WHO and the Center for Disease Control and Prevention in the U.S. and suggest that oseltamivir can be expected to be effective against any mutating influenza virus, which is the key to a pandemic,” said Professor John Oxford of Queen Mary’s School of Medicine and Dentistry, London.