Q & A: Defining Pandemic Flu The H5N1 bird flu virus is the main candidate for triggering a human influenza pandemic. The virus continues to stretch around the globe, with outbreaks as widespread as China, Nigeria and Scotland. NPR's editors Joe Neel and David Malakoff answer questions about the potential for a flu pandemic and the status of influenza treatments and vaccines.

Q & A: Defining Pandemic Flu

The H5N1 bird flu virus is the main candidate for triggering a human influenza pandemic. The virus continues to stretch around the globe, with outbreaks in birds as widespread as China, Nigeria and Germany. NPR health editor Joe Neel and science editor David Malakoff answer questions about the potential for a flu pandemic and the status of influenza treatments and vaccines:

Q: When officials talk about pandemic flu, what are they actually referring to?

A: There are three strains of flu commonly talked about right now.

One form is seasonal flu, which happens every year in the United States, killing 36,000 people annually.

A second strain is bird flu. Avian influenza occurs naturally among birds. The viruses don't usually infect humans. However, in 1997, a lethal strain of bird flu known as H5N1 appeared among humans in Hong Kong. Eighteen people were hospitalized and six people died. All of them had had close contact with poultry.

H5N1 resurfaced in Hong Kong in 2003, killing one person. Since then, cases of human infection with the bird flu virus have been reported in several countries, including Cambodia, China, Indonesia, Iraq, Thailand, Turkey and Vietnam. Several other countries have discovered H5N1 in birds, but not in humans. So far, there have been very few, if any, cases of H5N1 passing from one person to another.

Then, there's pandemic flu. There is no pandemic strain in circulation right now. The H5N1 bird flu strain is causing concern about the possibility of a pandemic; if it transforms itself into a human influenza virus, it could become very lethal to people and could spread rapidly around the world within several weeks to months.

Q: How many human infections of bird flu have there been?

A: As of April 2006, there have been 192 confirmed cases of humans infected with the H5N1 bird flu strain; 109 people have died, according to the World Health Organization (WHO). Almost all human cases have been traced to close contact with infected poultry.

However, it's impossible to know how many people have been exposed to the virus. In many parts of the world, farmers live alongside their poultry, and some health experts suspect that human cases of bird flu have gone unreported. China -- which has had numerous outbreaks of avian flu among birds but few reported infections among humans -- has threatened punishment for failing to report human cases.

Q: Can you get bird flu by eating infected birds?

A: There is no evidence that you can become infected by eating infected birds that have been cooked completely at normal cooking temperatures. Infected birds and eggs are unlikely to get into the food chain in the United States, according to the U.S. Department of Agriculture. And even if they did, safe handling and cooking of infected poultry meat and eggs would make the risk of infection negligible.

Q: Haven't there already been reports of bird flu in North America?

A: Yes, in Canada, but that's a different strain of bird flu, and one that's not as dangerous as H5N1. There are many bird flu viruses, and even many different forms of the H5 virus. So far, the H5N1 virus has yet to show up in North America.

Q: Will the H5N1 virus reach North America this year?

A: Experts say they wouldn't be surprised if it did. Many are betting that a wild bird, possibly a duck, goose, or swan, will carry it in from Asia or Europe as they head back north in the spring to nesting grounds in the Arctic or subArctic. Possible arrival points include far western Canada, Alaska and parts of the U.S. Rockies, or far eastern Canada and northern New England.

Q: What's spreading bird flu?

A: The H5N1 virus appears to be moving around the world several ways, and not all its paths are well understood. Basically, the two major known routes are the highway and the flyway.

Highway: Poultry farmers who move infected live birds, dead birds, chicken feces, contaminated crates, or even feathers and farm equipment can spread the virus. That may be why some outbreaks have been seen along major trade routes in Asia.

Flyway: Migrating wild birds also are moving the virus, although it is still not clear which birds are most involved. Also, bird migration isn't very well understood, and it can be very hard to track viral movement in the wild.

Q: If bird flu starts circulating among poultry in North America and Europe, is there any reason to believe that outbreaks in humans might be less likely?

A: That's possible. Poultry production in developed countries is quite secure and can be made even more secure if H5N1 shows up to any great extent. Farms are enclosed, so that contact with migratory birds is rare. Travel between farms is also controlled, making it less likely that a poultry worker would carry the virus from one facility to another. The European Union and local governments have already taken steps to limit the movement of poultry in countries with reported bird flu cases. If there are fewer opportunities for bird flu to spread amongst poultry, then the risk to human populations is lower.

Q: The U.S. government has released a plan detailing how it would handle an outbreak. What is the actual risk that there will be a pandemic this year?

A: That's impossible to predict. The H5N1 virus now present in birds must acquire several genetic changes before it's a threat to humans. Once it acquires those changes, it will be able to jump from human to human. So far, there's no evidence that this has occurred. However, the influenza virus changes its genes all the time. As birds with flu interact with humans and other animals, it increases the chances that the H5N1 virus will pick up the genes it needs to become a human virus.

Q: Is there a vaccine for bird flu?

A: Birds are getting vaccinated against H5N1 in countries such as China and Vietnam. Experimental vaccines for humans have proved safe, and they produce an immune response. But there is no way to test whether the human vaccine prevents bird flu at the moment because cases of bird-to-human transmission are still quite rare. The human vaccine still must undergo further study before it's approved by the Food and Drug Administration (FDA), but companies are already ramping up production.

Q: Is there a vaccine for pandemic flu?

A: No. The bird flu virus that has infected a few dozen people in Asia and the Middle East is not the same as the one that would ultimately create a human pandemic. Since it's not known what the pandemic flu virus will look like, a vaccine against it can't be made yet.

If pandemic flu appears, it will take months using the current egg-based production system to develop a new and effective vaccine -– a period during which millions of people will become ill and many will die. Scientists hope that the H5N1 vaccines now undergoing trials will provide at least some protection against the ultimate pandemic strain.

One U.S. study has shown that a vaccine produced using cells is safe in humans and that it stimulates an immune response. Growing cells in vats is much quicker than waiting for the flu virus to grow in chicken eggs –- a process that takes several weeks for each dose. If the current experiments are successful, flu vaccine production will be greatly speeded up.

Q: Once you have flu, are there any available treatments?

A: There are two drugs available to treat seasonal flu: Tamiflu and Relenza.

It's unknown whether Tamiflu or Relenza will work against a pandemic flu strain. As with a vaccine, until the pandemic strain appears, there's no way to test it.

For seasonal flu, Tamiflu comes in a capsule and Relenza comes in an inhaler. (There's a liquid formulation of Tamiflu for children.) If either drug is taken within the first 48 hours after symptoms appear, the length of the illness will be shortened by a day or two, and the severity of illness may also be decreased. Left untreated, flu can last 1-2 weeks.

Tamiflu can be taken by anyone over age 1, according to the drug's maker, Roche. Relenza, made by GlaxoSmithKline, is only for those age 7 or older and should not be taken by people who have breathing problems like asthma or other chronic lung diseases.

Q: Can I get a supply of Tamiflu or Relenza now, just in case?

A: Consult your doctor as to whether you need a prescription for one of these drugs. There has been a debate in the medical community over stockpiling them in case of emergency. Many physicians believe that stockpiling is unwise because of the risk that indiscriminate use of Tamiflu or Relenza could create drug-resistant strains of flu, whether it's seasonal or pandemic. There have been reports that seasonal flu may become resistant to treatment with Tamiflu, though that hasn't happened during this year's flu season. Other doctors feel that people should have the drugs if they want them.

In any case, there have been periodic shortages of Tamiflu. The manufacturer suspended shipments to U.S. pharmacies last fall when consumer demand increased because of pandemic fears. Shipments have since resumed, but there could be future shortages, however, because governments are ordering tens of millions of doses of these drugs.

One argument against stockpiling: It's not known whether Tamiflu or Relenza will be effective against a future pandemic strain of flu.

Q: Is there anything else individuals can do to prevent flu?

A: There are several common sense measures that can be taken to prevent the spread of any kind of flu. Flu viruses are spread in water droplets that emerge from coughs or sneezes. These droplets travel through the air and can be inhaled, or when they land on a surface, they are picked up by hands and can be rubbed into the eyes, nose and mouth.

If you're sick, cough or sneeze into tissues, or the crook of your arm instead of into your hand. The Centers for Disease Control and Prevention (CDC) recommends that those who are sick stay home from work, or if your children are sick, keep them home from school. To avoid catching the flu, avoid touching your eyes, mouth or nose, and avoid close contact with those who are sick. Regular handwashing is a must for everyone.