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Dr Margaret Chan

Director-General

Summit on business preparedness

for pandemic influenza

Video recording

31 January 2007

Assessment of the pandemic threat

Thank you, Michael, for that kind introduction. I value this opportunity to address such a distinguished audience of international leaders.

I know you are preparing the private sector to cope with the next influenza pandemic.

I hope the points I make will convey how important it is for people like you to lead the way forward.

You are meeting because of our shared concern that an influenza pandemic may be imminent. I can summarize the situation succinctly: nature has given us a strong and unprecedented warning. We would be foolish to ignore this warning or let our concern fade over time. We must stay on guard.

I will address two main issues.

First, I will provide an assessment of the present threat as perceived by WHO staff and the experts who advise us.

Second, I will describe what might happen during the first influenza pandemic of the 21st century.

Influenza pandemics are recurring events. They can be reliably documented beginning in the 16th century. Since then, each century has experienced, on average, three pandemics.

WHO has always been concerned about the recurring nature of influenza pandemics. Our network of flu labs was established in 1947, a year before WHO formally came into existence.

Pandemics invariably cause an abrupt surge in cases of illness, but mortality varies greatly. During the previous century, the pandemic that began in 1918 caused at least 40 million deaths worldwide. The one that began in 1957 was milder, causing more than 2 million deaths. The one that began in 1968 was even milder, causing around 1 million deaths.

Neither the timing nor the severity of the next pandemic can be predicted. But these events do inevitably recur, and they are always disruptive.

How serious is the present threat?

The highly pathogenic H5N1 avian influenza virus has been circulating in poultry in Asia since at least mid-2003. It has caused the largest outbreaks in bird and the highest number of human cases on record for any avian influenza virus.

No end is in sight. During these years, the virus has lost none of its persistence in nature, none of its virulence for humans.

In humans, the virus causes very severe disease, killing well over half of those it infects. For unknown reasons, most cases have occurred in previously healthy children and young adults. This was the pattern seen in 1918.

The H5N1 virus has fulfilled all prerequisites for the start of a pandemic save one: it does not, at present, spread easily from one person to another.

In September of last year, WHO brought the world’s leading influenza experts to Geneva to take stock of the current threat. Here are two main conclusions from that meeting.

First, the experts concluded that the seriousness of the present situation, including the risk that a pandemic virus might emerge, is not likely to diminish in the near future.

Second, this virus has evolved in alarming ways in domestic poultry, migratory birds, and humans in just the past four years. All of these changes are bad news.

Compared with viruses from the previous outbreak in Hong Kong in 1997, current H5N1 viruses survive longer in the environment and at higher temperatures, and are more lethal to chickens.

In humans, the case fatality rate in 1997 was 33%. In 2006, the case fatality rate was 70%.

In poultry, the virus has become firmly entrenched in large parts of Asia. The virus either stays put or comes back, as we are seeing right now in Japan. Control has proven to be extremely difficult, particularly where free-ranging backyard poultry are affected.

As an epidemiologist at our country office in Cambodia observed: You cannot ask poor rural households to bury their food. Almost all human cases to date have occurred following close contact with backyard poultry.

As another alarming development, we have lost one of our warning signals. Domestic ducks can now become infected and excrete large quantities of lethal virus, yet show no signs of illness.

Finally, we know that migratory birds can carry highly pathogenic H5N1 virus over long distances. Something called “relay” transmission has been documented. The virus moves from poultry to wild birds and then back again. This greatly increases its capacity to spread internationally.

As I mentioned earlier, this virus is not, at present, able to spread easily from person to person. How might this happen?

Transmissibility can improve via two mechanisms. The first is called reassortment. Influenza A viruses have eight neatly segmented genes. When a person or another mammal is co-infected with an avian and a human influenza virus, the two can exchange gene segments – shuffled like playing cards.

The result is a new virus that has both human and avian genes. If this new virus can infect humans, cause serious disease, and spread easily from person to person, it will spark a pandemic.

We now know that reassortment generated the viruses responsible for the 1957 and 1968 pandemics.

The second mechanism is known as adaptive mutation. This mechanism involves stepwise changes in the virus which occur during sequential infections of humans or other mammals. The virus gradually acquires mutations that make it more human-like. Genetically, it remains an entirely avian virus, and is thus entirely foreign to the human immune system.

This mechanism generated the virus responsible for the 1918 pandemic.

Many – but not all – scientists now believe that if the H5N virus acquires an ability to start a pandemic, it will do so through adaptive mutation.

The important point: each human case gives the virus an opportunity to change by one of these two mechanisms. This is why WHO follows each new case so closely.

I will now turn to the second question. What might we expect to see during a pandemic?

First, all countries will be affected. Global spread is inevitable, given the contagious nature of influenza. Countries might, through measures such as border closures and travel restrictions, delay arrival of the virus by some days or weeks, but cannot stop it.

Second, international spread will be rapid. The pandemics of the previous century encircled the globe in 6 to 9 months, even at times when most international travel was by ship. Most experts predict that global spread of the next pandemic will take place in around three months.

Third, widespread illness will occur. Population vulnerability to infection with a pandemic virus of the H5 subtype will be universal. Conservative estimates predict that around 20% of the total world population will fall ill. Worker absenteeism is likely to reach 35% of the workforce or higher, as workers stay home to care for ill family members or to protect themselves from becoming infected.

Fourth, excess mortality will occur. The number of deaths is influenced by properties of the pandemic virus, and cannot be predicted in advance.

But the next pandemic will be the first in a world weakened by the emergence of HIV/AIDS and the resurgence of malaria and TB. It is logical to assume that co-infection with these diseases would increase mortality, but we just don’t know for sure.

Fifth, medical supplies will be inadequate. Supplies of vaccines and antiviral drugs – the two most important medical interventions for reducing illness and deaths during a pandemic – will be inadequate in all countries at the start of a pandemic and for many months thereafter.

Sixth, hospital capacity will be inadequate. Current worldwide projections for the next pandemic estimate that some 6.4 million to 28 million people will require hospital care over a relatively short period of time. An estimated 1 billion people will fall seriously ill. Few countries have the staff, facilities, equipment, and hospital beds needed to cope with an abrupt surge in patients.

Finally, economic and social disruption will occur. High rates of illness and worker absenteeism are a characteristics feature of pandemics and help account for the great social and economic disruption they usually cause.

Pandemics spread globally in waves that rapidly peak, and then subside – much like a tidal wave. Not all parts of the world or of a single country will be severely affected at the same time.

Within a given community, the peak incidence of illness is expected to last from around 6 weeks to three months, depending on such factors as population density. Social and economic disruptions are therefore temporary, but may be amplified in today’s closely interrelated and interdependent society.

All of these factors make pandemics costly in terms of economic and social disruption as well as human lives. In 2005, the World Bank estimated that a pandemic could cost the world economy around 800 billion dollars within a year. In late 2006, the World Bank raised that estimate to 2 trillion dollars in a worst-case scenario.

In conclusion, let me stress again that influenza pandemics inevitably recur. Everything we do to enhance preparedness – every research study, every national preparedness plan, every desktop exercise – allows us to cope better when a pandemic occurs – whether this is caused by H5N1 or another virus, whether this happens tomorrow or years away from now..

This same principle applies to the work on your agenda. I wish you a most productive meeting. I am sure all parts of our interconnected world will benefit from your conclusions.

Thank you.

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