Swine Flu: Your Questions Answered Just how dangerous is swine flu? What would going to a WHO pandemic Phase 6 really mean? Why is the flu seasonal? NPR's science desk answers these and other questions submitted by listeners and readers.

Swine Flu: Your Questions Answered

This is the H1N1 virus isolated from one of the California cases early in the outbreak. CDC hide caption

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This is the H1N1 virus isolated from one of the California cases early in the outbreak.


'Flu Shots' Blog

Get the latest updates on the swine flu outbreak.

Swine flu has been splashed across the news since its emergence last month, and it can be tough to sort through the abundance of information being circulated. NPR's science desk helps you navigate the outbreak by answering some of your questions:

How dangerous is this strain of H1N1?

It's a tricky question, because we don't know how lethal this new H1N1 really is. The first reports out of Mexico looked grim — a high death rate and rapid spread. But that was before the country had a real capacity to track the epidemic and calculate a death rate. As teams from the World Health Organization, the U.S. and Canada have brought in more testing equipment, the outbreaks in Mexico are looking less severe. But it will still be several days or weeks before enough tests have been completed in Mexico and the U.S. to determine how dangerous the virus is.

Is this more dangerous than seasonal flu?

Part of the confusion comes over the use of the word "pandemic." It's a term used by scientists to denote wide geographical spread — not how dangerous a disease is. At the moment, what we're seeing is the spread of a few cases over a wide area. What we're not seeing, at least yet, is one case spreading out from a central point and afflicting an entire school or community. This would mean that the virus is capable of easy and sustained spread between people. Also, we're not seeing an infection that appears more deadly than the regular seasonal flu.

In a normal year, anywhere from 5 to 20 percent of Americans get seasonal flu. It's not clear yet what proportion of people exposed to the new virus get sick, but it doesn't appear to be too far above the rate for regular flu.

As for how dangerous the new flu virus is, it appears that most people so far have relatively mild illness. But about 10 percent of recent confirmed cases in the United States have required hospitalization, and there's been one death. In a normal flu season, about 200,000 people are hospitalized and about 36,000 people die. It's still too early to say if swine flu is more or less dangerous than seasonal flu.

What would it mean if the WHO raised the level to a full-scale pandemic (Phase 6)?

The pandemic phases indicate how the virus spreads among people. Phase 5 is where we are now — a pandemic may be "imminent." It means that at least two countries in a region — in this case, North America — have documented spread from person to person of a new virus. Phase 6, a full pandemic, would only occur if the WHO decides there is solid evidence of spread from person to person in another region of the world. It looks like it might be Europe next, though there are a few cases in South America and Asia.

Homeland Security Secretary Janet Napolitano said Sunday that the WHO pandemic level might be raised this week. But so far in Europe, the cases have not spread among communities, and the WHO says there are currently no plans to declare a pandemic.

Why is flu seasonal?

The seasonal rise and fall of the flu is a decades-old pattern. A few recent studies by researchers at the Mount Sinai Medical Center in New York City found that the flu virus transmitted more effectively in colder, drier temperatures. When a sick person coughs or sneezes, droplets of moisture containing the virus spray into the air, and in low humidity they dry out quickly, become smaller and stay in the air longer. This means there is more of the virus in the air for you to inhale.

And, scientists think the quality of the mucous in the throat might be different in the winter, which affects how the virus lands in your respiratory tract. There might also be other environmental factors or human body (host) factors that scientists don't understand yet.

It's autumn now in the Southern Hemisphere, and both the WHO and the CDC are watching closely to see how the flu progresses as this part of the globe moves into winter. In the tropics, flu isn't seasonal and occurs all year, usually at lower levels than in the temperate zones where most people live.

When will the first batch of vaccine be available? Will we need to get seasonal flu shots in addition to the swine flu vaccine?

If everything goes according to plan, federal health officials hope the first doses of the new swine flu vaccine will be rolling off the production lines in mid-September. There would be enough supply for everyone, according to federal officials, but not all at once. It's likely that first responders like health workers, law enforcement officers and other people in critical jobs would get it first. It would take until early 2010 before enough could be produced for all Americans.

The plan would be to also administer both the new swine flu and the regular seasonal flu vaccine next fall and winter. Ordinary flu viruses will still be circulating, and health officials don't want to leave everybody unprotected against those.

It's not clear yet whether a single vaccine could be made combining the swine flu vaccine and a seasonal vaccine (which protects against three different flu strains). No one has made a 4-in-1 vaccine before. And it's possible that people will need two shots of the swine flu vaccine in any case.

Whatever the plan, it's going to take an unprecedented effort to produce the vaccine, get it distributed, and get a substantial fraction of the U.S. population vaccinated against both seasonal and the potential pandemic flu.

What are the chances this was a virus made in a lab? I've heard it's an odd mixture of swine strains from three different continents, plus bird, plus human.

We don't know of any scientist, inside or outside the government or World Health Organization, who believes the new H1N1 swine flu virus was man-made. Although this virus is a unique combination of flu viruses (swine, bird and human), these "reassortant" viruses do occur regularly in nature. Pigs are natural "vessels" for these gene-swapping events, because their cells contain receptors for human, bird and swine viruses.

There may have been an H1N1 flu virus that escaped from a lab. But if that happened, it occurred in the late 1970s, perhaps from a lab in northern China or the Soviet Union. Some scientists think such an incident may have reintroduced an H1N1 strain into humans. It was a strain of H1N1 that touched off the great flu pandemic of 1918-19 and circulated, in a less virulent form, until 1957. Since 1977, H1N1 viruses have regularly caused seasonal flu outbreaks.

It is important to keep in mind, as you follow this story, that H1N1 is not a single flu virus. Nearly 12,000 members of the H1N1 family have been identified. The new swine flu virus is just the latest one, and no one knows what kind of threat it represents.

Is swine flu widespread in Mexico? Mexico City? Have there been outbreaks at the resorts?

There have been cases in most parts of Mexico, with the highest number of confirmed cases in the central interior regions of Mexico City, Estado de Mexico, San Luis Potosi and Hidalgo. The majority of these cases have occurred in previously healthy young adults, according to the Pan American Health Organization. Researchers are still trying to determine why some Americans who visited resort areas in Mexico came back with the flu, since major outbreaks have not been reported in these areas. So it's not possible to answer this question completely until more is known.

Why was there confusion over the number of deaths in Mexico?

There evidently was limited capacity in Mexico to do the new kinds of testing needed to confirm swine H1N1 flu cases until the weekend of April 25-26. That's when a team from the WHO arrived with test kits to permit more testing and faster results. Prior to this, the test was only available in three labs in the U.S. and Canada, and three labs overseas. As scientists go through the samples that were on hand and collect more samples for testing, the data are getting more reliable. As of May 5, there were 757 cases confirmed in Mexico, with 26 deaths. Prior to this, estimates were all over the place, and it wasn't possible to calculate how lethal the virus is. We still won't hear an estimate of this for several days or even weeks. If you want to learn more about the test, you can read about it here.

What's the definition of a "probable" and "confirmed" case?

The CDC has specific definitions for these words:

Confirmed refers to a person with a fever and coughing or shortness of breath who has been confirmed by laboratory tests to be infected with the swine flu virus.

Probable refers to a person who had a flulike illness (fever, coughing, shortness of breath) who has tested positive for influenza A, but is not positive for either of the Type A flu viruses that have been circulating this winter. The vast majority of these "probable" cases will later be confirmed as swine flu.

Suspected refers to a person with a flulike illness (fever, coughing, shortness of breath) who also meets one of the following criteria:

  • Became ill within seven days of close contact with a person with confirmed swine flu.
  • Became ill within seven days of traveling to a community with at least one confirmed swine flu case.
  • Lives in a community with at least one confirmed swine flu case.

Other news organizations use descriptions including "possible," "presumed," "likely," etc. NPR tries to stick with the terms used by public health officials, as much as possible, to limit any confusion.

If sick with swine flu, how long should you stay home from work?

The CDC recommends that you should stay home at least seven days from the time you first experience flulike symptoms, or until you have been symptom-free for 24 hours, whichever is longer. You shouldn't visit a school during that time either, according to the CDC's recommendations. At home, you should keep the sick person in a room separate from the common areas of the house, if possible. The sick person should not have visitors, except for a caregiver. Check with your health care provider about taking antiviral medications.

Are hand sanitizers useful?

The CDC suggests that people clean their hands often, using soap and water or an alcohol-based hand rub. The idea isn't just to protect you, but to protect others in case you are infected. So, according to the CDC, you should be vigilant about washing your hands if you cough or sneeze into them. Paper towels are preferable for drying your hands, especially if you are sharing a home or work space with someone who is or might be infected. It is widely accepted by health professionals that washing your hands often can reduce, but not eliminate, the likelihood of getting infected.

Which professions are most vulnerable?

Any profession that puts you in contact with people likely to have the flu will raise your chances of getting infected. Health care workers are clearly exposed to people with the flu, but emergency medical workers may also face higher risk. Teachers work in crowded conditions with children who might be infected; the median age of swine flu victims is, at the moment, 16. Airlines are taking special precautions for their flight crews because they also are in close contact with lots of people in a confined space. Cruise ships may also bring people from various parts of the world into confined spaces for prolonged periods. The CDC has issued a special guidance for people in the airline and cruise ship industries, as well as emergency medical workers.

-- With reporting by Joe Neel and Christopher Joyce