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INDEPTH: AVIAN FLU
Antivirals and avian flu
CBC News Online | October 26, 2005

Romanian health worker carries birds before gassing them in the village of Vulturul. (AP photo)

There are two ways to protect people from the effects of a disease like avian flu: treat the symptoms of the disease after infection, or prevent infection in the first place.

In the case of the flu, the prevention takes the form of vaccines, and the treatment the form of antiviral drugs.

Vaccines cause the production of antibodies against a virus prior to being infected. When an immunized person is exposed to a person with influenza the antibodies generated in response to the vaccine are ready to attack the virus as it enters the body and prevent illness.

But avian flu is not a disease that is generally passed directly from one person to another, so a vaccine would be of limited use. Scientists are concerned avian flu could mutate into a contagious form that passes from person to person, but it's impossible to make a vaccine for a virus that hasn't been identified, let alone one that doesn't even exist yet.

Antiviral drugs

Antiviral drugs like Tamiflu and Relenza work to block the flu virus from escaping an infected cell and spreading further. This helps to ease flu symptoms and reduce the duration of the illness.

The catch is that the antiviral drug must be taken very soon (often within 48 hours) after an infection is suspected. That's before most flu symptoms become evident. There is also a risk that if the drugs are widely used, viruses will begin to mutate to resist the medication.

There are currently only four antiviral drugs marketed to battle the flu: oseltamivir (Tamiflu) and zanamivir (Relenza), which are neuraminidase inhibitors; and amantadine and rimantadine, which are called adamantane drugs. Rimantadine is not sold in Canada, and both amantadine and rimantadine are older drugs that new influenzas are more likely to develop a resistance to.

Tamiflu is sold in pill form while Relenza is a powder administered using an inhaler and patients have to be taught how to use it. Relenza has never been a big seller in North America. It doesn't have as long a shelf life as Tamiflu, but it would be effective in a pandemic. Germany has put in a large order for this drug because they couldn't get Tamiflu.

Tamiflu can be used two ways, as a treatment when someone is sick with the flu and as a preventive to keep people who have likely been infected, such as health-care workers, from getting sick.

Unfortunately, Tamiflu has a guaranteed shelf life of only five years, and there is a risk that widespread use among patients could lead to resistant strains of the flu.

Availability of Tamiflu

In a perfect world, we'd all have enough Tamiflu to take one pill every day that the pandemic virus is circulating in our region. One pill protects you for one day. Based on the history of other pandemic influenzas, experts believe the first wave in a given area would last up to 100 days. So if you were trying to protect yourself from infection, you would need to stockpile about 100 doses of Tamiflu and start taking them from the moment you hear the virus is circulating in your region.

If you're a government right now trying to stockpile millions of doses of Tamiflu and you want them tomorrow, you're not getting them. Political pressure is mounting to find ways to produce more Tamiflu more quickly.

The World Health Organization has advised those governments that can afford Tamiflu to stockpile it. Canada was one of the first out of the gate and has purchased 35 million doses and ordered 5 million more. Officials say that should be enough to treat 3.5 million people including those who are already infected and essential workers, to protect them from becoming infected.

But most developing countries, including those that have seen cases of bird flu in humans, can't afford to stockpile, and even if they could, supply is becoming an issue.

There is such a great demand for Tamiflu that the manufacturer, Roche Pharmaceuticals, stopped selling the drug to pharmacies in late October 2005. Roche said it wanted to safeguard its supply for the upcoming flu season. Roche has also licensed several generic drug companies to produce the drug.

The company won't disclose how much Tamiflu it's able to make every year, but some countries like the U.S. have been told it could take a decade to fill all their orders. Now some are suggesting the pandemic threat has reached a point where governments should step in and override the Tamiflu patent, let generic companies make it, too.

If there were a shortage during an outbreak, governments could likely override the Roche patent and produce the drug generically in order to meet the demand. A generic drug maker in India announced in October 2005 that it would ignore the patent and produce generic Tamiflu. The generic copy would be sold to Third World countries that can't afford the brand name version. In the same month, Taiwan announced it was starting work on its own version of the drug.

Faced with these threats, Roche is now signalling a willingness to allow other companies to make Tamiflu without giving up its patent and presumably its profits.

In a release from its CEO, Roche says: "In support of the global effort to fight a potential pandemic, we would be prepared to discuss such sub-licences to increase the manufacturing of Tamiflu."

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INFORMATION:

Public Health Agency of Canada for the public:

Tel: 1-800-484-8302
Email
Local Health Canada phone numbers

QUESTIONS:

Send us your questions about bird flu. We'll get the experts to answer them.

PREVENTING THE FLU

What you can do:

Get a flu shot. There is no vaccine for avian flu but it may boost your overall immunity, health officials say.
Wash your hands to wash away the flu virus
Cover your mouth when you sneeze or cough
Stay home if you are sick.
More on what you can do here

QUICK FACTS:

Definition:The flu is a contagious respiratory illness caused by influenza viruses. It can cause mild to severe illness, and at times can lead to death. Bird flu is an infection caused by avian influenza viruses. (Source: CDC)

Symptoms of flu/avian flu:Fever, fatigue, cough, sore throat, eye infections, muscle aches.

Transmission:Infected birds shed flu virus in their saliva, nasal secretions and feces. Avian flu may have passed to humans by contact with infected poultry or contaminated surfaces. In human-to-human cases, flu viruses spread in respiratory droplets caused by coughing and sneezing. (CDC)

Prevention:Get a seasonal flu shot, wash your hands, cover your mouth when sneezing, stay home if you are sick, consult your doctor.

Avian flu vaccine:It is under development but cannot be finalized until the pandemic version of the virus appears.

Cure: A healthy body's immune system can often combat the flu. Antiviral drugs may help. Antibacterials are ineffective because the flu is a virus.

VACCINE & ANTIVIRALS:

DEFINITION
Vaccines and antivirals are different. A vaccine is designed to procure immunity from a disease. An antiviral drug is commonly used to treat an existing illness. Antivirals can also be used in a preventive way, but they are not vaccines, and do not provide immunity.

EXTERNAL LINKS:

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Cumulative Number of Confirmed Human Cases of Avian Influenza A/(H5N1) Reported to WHO

Canadian Food Inspection Agency avian flu

Canadian pandemic influenza plan

Public Health Agency of Canada

Latest information for travellers from the Public Health Agency of Canada

WHO avian influenza

WHO - estimating the impact of the next influenza pandemic

U.S. Centers for Disease Control - Avian flu

UN Food and Agriculture Organization Avian Influenza site

World Organization for Animal Health

EU Avian Flu site

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