Stuart Johnson, Deseret Morning News
Russell Clark, 104, of Orem, recalls 1918 epidemic's effect on his family.

"Pandemic" strikes fear in people who know what the word means, and health experts say it's lurking somewhere in the future — possibly very soon.

A deadly avian flu affecting poultry in eight Asian countries this year has already been transmitted to some humans. If it starts spreading person to person, it could be devastating, health experts warn.

Any flu outbreak is called an epidemic. A pandemic occurs when a new form of influenza or an old one against which people have no antibodies breaks out. Past pandemics have killed thousands and even millions.

A World Health Organization bulletin contains a sober warning: "WHO believes the appearance of H5N1, which is now widely entrenched in Asia, signals that the world has moved closer to the next pandemic. While it is impossible to accurately forecast the magnitude of the next pandemic, we do know that much of the world is unprepared for a pandemic of any size."

"It's hard to quantify the risk" of pandemic, said Dr. Patrick Luedtke, state deputy epidemiologist. "A pandemic will probably happen at some point. Will it be our lifetime or our children's? We don't know. . . . It will be how we respond to it that matters most."

"It's just the nature of the virus," said Salt Lake Valley Health Department epidemiologist Ilene Risk. "Influenza Type A has the ability to rapidly change and cause more severe disease, so it could happen."

Worldwide, health experts are gearing up in case the current Asian outbreak of avian flu starts spreading from person to person. Avian flu has killed 45 people so far, all of whom contracted it from birds. Testing is about to begin on an experimental vaccine, disease surveillance is moving into high gear and the U.S. government is stockpiling anti-viral drugs and vaccine.

The next pandemic

The World Health Organization has estimated that the next pandemic is likely to kill between 2 million and 50 million people. Because a pandemic is typically caused by a new form of virus, its real magnitude can't be predicted.

The mechanics of a pandemic seem deceptively simple.

Influenza A viruses all have two proteins on their surface, hemagglutinin and neuraminidase (the "H" and "N" health experts use to show which flu strain is going around). There are many subtypes of each — 15 H's and nine N's — that can combine in various ways to create a different virus. Not all attack humans.

The Centers for Disease Control and Prevention say that flu viruses are always changing. Both types A and B make small changes, called antigenic drift, that over time produce new strains the immune system doesn't know, which can lead to reinfection. The body is smart and gets busy making antibodies, then more changes occur. It's a cycle.

The mutation that brings a killer pandemic, antigenic shift, is an "abrupt, major change" in influenza A viruses, altering the H proteins and sometimes the N proteins to create an influenza A strain so different and unexpected that most people have little or no antibodies to fight it, according to the CDC.

Drift is continual, shift is occasional.

Even a shift won't cause a pandemic unless the new strain is easily spread among humans and also causes severe illness.

Influenza A viruses, the only type to cause a pandemic, are found in lots of animals, but B sticks with humans.

The past two pandemics were combinations of bird and human flu viruses. The National Vaccine Program Office says many people believe the pandemics emerged when an intermediate host, possibly a pig, was infected by both human and bird viruses at the same time, creating a new virus that spread easily to humans, who had no antibodies to protect them.

Deseret Morning News graphicDNews graphicInfluenza primerRequires Adobe Acrobat.

The Hong Kong virus of 1997 erupted when a novel virus "jumped" the species barrier and humans caught the avian flu.

A pandemic can also result from recirculation of a virulent virus that hasn't been around for a long time. That's likely to spare the elderly, who at some point developed antibodies, compared to its ravages on younger, normally healthy people. An example of that was the flu of 1918, which stayed a few years then disappeared, not reappearing noticeably in people until 1977, although it may have sickened a few people here and there in the years between.

As bad as 1918 was, the virus then was apparently similar enough to one that circulated in the late 1800s that some of the elderly exposed to it had some antibody protection when the pandemic struck.

Being prepared

Historically, pandemics have been very different from flu epidemics in another key way: whom they ravage most. Were someone to draw a graph of deaths in a typical flu epidemic, it would be somewhat U-shaped, since the people hardest hit and most likely to die are the very young (especially under 6 months) and the elderly. The pandemic graph would look like a W — the very youngest and oldest die, but so do folks in the middle, ages 20-49.

"One of the issues we're concerned about, with the W-shaped curve, is it includes some of those responsible for keeping society going," Luedtke said. "We will have to determine what to do with limited vaccine and antivirals. Who do we vaccinate and treat first? And it could be the next pandemic strain doesn't target that group. Maybe it will be different, like everyone with cardiovascular disease."

If a pandemic suddenly occurred, it's unlikely a vaccine could be made quickly enough to help much initially, Risk said.

It takes about five months from identifying a strain to producing a vaccine, Luedtke said. Past history indicates that won't help the first people to become ill, but a pandemic occurs in waves. In the first wave, about 25-35 percent of those exposed become sick. A few weeks later, a second wave affects 5 to 10 percent of those exposed.

Utah's likely to be lucky there, since it's doubtful the first breakout would occur here. It's more likely to hit elsewhere — "probably in Southeast Asia, where they have problems with avian influenza," Luedtke said. It's possible the flu strain could be used to make a vaccine before it even hit Utah.

Fear of pandemic has led health departments to year-round surveillance, said Luedtke, something the Utah Department of Health started last year. Many states, including Utah, have developed a pandemic plan. All states that accept a federal bioterrorism grant will have to have one this year.

Utah's plan focuses on the same five areas outlined by the Health and Human Services Department pandemic response plan released in August, starting with what the military calls "command and control." That sets out who's in charge and how the state's health experts would set up a management center. Next comes epidemiological response, including how to do enhanced and active surveillance. The third point deals with vaccination and antiviral medication distribution. It takes coordination to get the vaccine out to local health departments and to decide the best way to use the limited amount of antivirals, Luedtke said.

The plan addresses how the state will deal with a large number of people who are all sick at once, including how to use existing facilities and what would become alternative facilities.

The last point is communication, starting with production of preprinted recommendations on what people should do if they're sick and how to care for themselves and loved ones, as well as already produced messages the media will be given to help get the word out.

The plan also parallels other federal responses, including the National Response Plan released by the Department of Homeland Security in December, Luedtke said.