From Our 2009 Archives

Swine Flu Pandemic FAQ

What the swine flu pandemic means to you.

By Daniel J. DeNoon
WebMD Health News

Reviewed By Louise Chang, MD

Swine flu is pandemic, the World Health Organization (WHO) has declared.

The declaration does not mean that swine flu -- aka novel influenza 2009 type A H1N1 -- is any more deadly today than it was yesterday.

A pandemic sounds scary. But what does it really mean? Here are answers to your questions.

Questions about swine flu? See our swine flu FAQ.

What is a pandemic?

A pandemic is a new infectious disease that spreads around the world.

The best recent example of a pandemic is AIDS, caused by a virus new to humans: HIV.

Seasonal flu viruses spread around the globe and cause 250,000 to 500,000 deaths each year -- including some 36,000 annual deaths in the U.S. But seasonal flu isn't considered a pandemic, even though the viruses that cause them change a little from season to season.

One of the seasonal flu viruses is a type A H1N1 virus. But the type H1N1 swine flu virus that appeared in 2009 is an entirely different virus. It carries genes from swine flu viruses from North America and Eurasia as well as genes from human and bird flu viruses.

Humans have never before been infected with this virus. That means that nobody is immune, although some people born before 1957 may have been exposed to an ancestor virus that could possibly give them a small degree of protection.

Because the vast majority of people are vulnerable to the 2009 H1N1 swine flu virus, because it spreads easily from person to person, and because the virus is spreading in communities in different parts of the world, the current swine flu has reached pandemic proportions.

Flu pandemics occur regularly. That's because there are many kinds of flu viruses in animals (mostly birds), but so far only a few have evolved the ability to infect humans. There were three flu pandemics in the 20th century: in 1918, in 1957, and in 1968.

What does the WHO pandemic alert mean?

The World Health Organization has declared the 2009 H1N1 swine flu to be a pandemic.

That does NOT mean that swine flu is more dangerous than it was before. The declaration means only that the WHO officially recognizes that swine flu is spreading globally -- and that countries that have not yet put their flu-pandemic plans into action should do so now.

Swine flu already has been spreading in the U.S., so the WHO declaration makes very little difference. U.S. health officials already have been working furiously to prepare for the fall 2009-2010 flu season.

Why has WHO declared a pandemic now?

WHO's technical criteria for declaring a pandemic is that the infection must be spreading locally in at least two distinct regions of the world. That actually went on for some time before the official declaration. But the WHO was worried that governments might overreact to a pandemic declaration.

They had good reason to think so. Early in the pandemic, some countries stopped importing pork and even slaughtered local pig herds -- even though the so-called swine flu is spread from person to person and cannot be spread by eating pork. And other nations established unreasonable travel restrictions or unnecessarily quarantined healthy people from countries where the flu was spreading.

These unnecessary actions had serious economic and social impacts. And since most public health experts feared that the next flu pandemic would be the vastly more deadly H5N1 bird flu, most pandemic preparedness plans contained steps far more drastic than steps needed to fight swine flu, which is only moderate in severity.

The six-stage WHO pandemic alert system does not take disease severity into account; it's based on the geographic spread of a virus.

The CDC does have a pandemic severity scale, which has five categories. The scale is based on the percentage of infected people who die -- the case-fatality ratio.

It's too soon to know the case-fatality ratio for H1N1 swine flu. But the CDC's best estimate so far is that it is 0.1%. That puts it on the borderline between Category 1 (the lowest category) and Category 2. The 1918 swine flu was a Category 5 pandemic, with a case-fatality rate of over 2%.

Even a Category 1 pandemic is serious. The CDC estimates that a pandemic with a 0.1% case-fatality ratio would result in some 90,000 U.S. deaths if no vaccine becomes available.

Has H1N1 swine flu become more dangerous?

No. So far, the H1N1 swine flu virus that is spreading around the globe is very similar to the swine flu viruses first seen in North America.

Experts say the disease is moderate in severity. That is because most cases -- and most hospitalizations -- have been in young people 5 to 24 years old. A small proportion of these young people have died.

Even though most people who get swine flu recover fully, these troubling deaths in otherwise healthy young people make experts hesitate to call the disease "mild."

Flu viruses do, of course, mutate. They may become less dangerous. But they may become more deadly, possibly picking up virulence factors from other flu bugs circulating at the same time. The nightmare scenario is that the H1N1 swine flu would combine with the H5N1 bird flu to create a fast-spreading, lethal virus. But the chance of this happening is small.

And pandemics come in waves. They tend to appear, wane, and reappear over two or three years. Sometimes there may be a mild first wave, followed by far more serious waves. That's what happened in 1918 and 1919 -- and that's what keeps public health officials awake at night.

Am I less safe now that swine flu is pandemic?

No. In fact, the world likely is more safe now that all nations will be taking appropriate actions to limit the impact of the H1N1 swine flu pandemic.

What should I do now that a pandemic has been declared?

The pandemic alert is a good time to check your family and community preparedness plan.

If you don't know your community plan, check with local heath officials. Let them know if you think you might be able to volunteer in case your help is needed. Even a mild flu could disrupt local services if a large number of people fall ill.

And if you don't have a family checklist, it's time to make one. The CDC offers guidance at its pandemicflu.gov web site.

When will the pandemic end?

Most pandemics end when enough people become immune to the disease -- either because they've survived infection or because they've been vaccinated.

Past pandemics have lasted two or three years. This time, the pandemic may be shorter.

That's because the world has steadily been building up its ability to make flu vaccines -- and because the new H1N1 swine flu virus was discovered and isolated in record time.

It's possible that a successful vaccination campaign could significantly shorten the pandemic. Whether this will happen remains to be seen.

Interestingly, pandemic flu viruses don't go away when the pandemic ends. Often they stick around to become a new seasonal flu bug, replacing one of the seasonal viruses.

What is the government doing about the pandemic?

There's been a strong response by the U.S. federal government to the swine flu epidemic. State and local responses have been vigorous, but in many areas have been -- and will be -- hampered by budget cuts to health departments.

The federal Department of Health and Human Services and Department of Homeland Security are working extremely hard. These efforts have focused on preparing to assist state and local responses and on developing a swine flu vaccine.

The vaccine effort is very complicated. Early steps have gone well. The CDC has isolated and given to vaccine manufacturers a "seed virus" that can be used to make a vaccine. Now manufacturers are working to make an actual vaccine.

Once there's a first lot of vaccine, the National Institutes of Health will test it on human volunteers to see if it seems to work -- and if it seems to be safe.

Meanwhile, the U.S. government has purchased bulk materials for commercial-scale vaccine manufacture. Purchase of needles and syringes will follow. But the big questions -- whether to go ahead with full-scale vaccine manufacture, who should be vaccinated first, and how the vaccine will be distributed -- remain to be answered.

SOURCES: WebMD Swine Flu Guide. World Health Organization web site. CDC web site. Pandemicflu.gov web site.

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