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Pandemic risk remains despite bird flu find

A young girl under observation for the bird flu virus in Indonesia Keystone

Swiss health officials say the risk of a bird flu pandemic remains despite new research explaining why the H5N1 strain does not pass easily between humans.

This content was published on March 23, 2006 - 21:32

Scientists in the United States have found that the deadly avian virus tends to sit deep within the lungs minimising the risk of it being spread through coughing or sneezing.

Human flu viruses on the other hand prefer to infect cells in areas like the nose and windpipe, thereby increasing the risk of transmission. But the Federal Health Office warns that this behaviour could change if the H5N1 virus mutates.

Patrick Mathys, an epidemiologist at the health office, told swissinfo that the findings offered a possible explanation for the small number of human cases over the past couple of years.

"This means that the virus load when you sneeze or cough is obviously too small to infect people," he said.

"This is not bad news at all but you cannot say we are safe now. We still think H5N1 has the potential to mutate into a pandemic strain."

The H5N1 virus has killed more than 100 people and infected over 180 worldwide since it re-emerged in late 2003.

People infected with the virus have virtually all been in close contact with diseased birds but scientists fear it could mutate into a highly infectious pandemic strain that could kill millions.

So far avian flu has been found in 24 wild birds in Switzerland but there have been no human cases.

New developments

The discovery, published in the journal Nature on Thursday, comes just days after another more worrying development earlier in the week.

On Monday researchers from the US Centers for Disease Control and Prevention said the H5N1 virus had evolved into two separate strains.

The health office described the announcement as "bad news" for the development of a vaccine.

The Swiss government has placed an order with France's Sanofi Pasteur for 100,000 doses of a pre-pandemic vaccine against H5N1. The intention is to distribute these to frontline workers dealing with infected birds.

"As soon as you have two strains you probably have to develop two strains of a vaccine as well, and this could make it more difficult to have a vaccine ready against H5N1," warned Mathys.

Infectious diseases

Christian Ruef, associate head of infectious diseases at Zurich University Hospital, told swissinfo that it was to be expected that the virus would evolve.

"That's what happens with normal flu strains. They are quite unstable and we get mutations throughout the year, and over the years we get small shifts. For example, the vaccine we use for normal human flu does not completely or optimally cover strains that are circulating now," he said.

Ruef said that when a pandemic arrived one strain of bird flu was likely to prove dominant and drugmakers would direct a vaccine against this virus.

Mathys added that the Sanofi vaccine was still going through clinical trials and was unlikely to be ready until later this year.

But he said that if bird flu was to spread among Swiss poultry flocks before the drug had been cleared, the government might decide to use it anyway.

"If the situation worsens and we have mass outbreaks in poultry in Switzerland and we have to protect the personnel culling poultry then we will probably buy the vaccine at a stage when not all clinical trials have passed," he said.

"If some clinical trials are missing it's really difficult to say whether the vaccine is 100 per cent safe or whether it works. You can probably say it's safe based on what we've seen so far but whether it protects you very well against the circulating H5N1, you can't say."

swissinfo, Adam Beaumont

In brief

Swiss pharmaceutical firm Roche said last week it was increasing production of its anti-viral drug Tamiflu by a third to meet increased demand.

Basel-based Roche said it would lift capacity by an additional 100 million treatments to a total of 400 million treatments by the end of the year, after striking deals with external producers.

Switzerland has reported 24 cases of avian flu among wild birds. No domestic fowl have been infected.

All poultry has been kept indoors since February 20, but the Federal Veterinary Office has no plans to vaccinate domestic birds.

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Key facts

The Swiss government has ordered 100,000 doses of an H5N1 "pre-pandemic" vaccine for frontline workers. This should be delivered by the end of 2006.
Work cannot begin on a vaccine until a pandemic starts and scientists know the strain of virus they are up against.
According to the Geneva-based World Health Organization, such a vaccine could take 6-9 months to develop.

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