Expert says the world is not ready for the next pandemic

Michael T. Osterholm is Director of the Center for Infectious Disease Research and Policy, Associate Director of the Department of Homeland Security's National Center for Food Protection and Defense, and Professor at the University of Minnesota's School of Public Health.

He has written at length in the July/August 2005 issue of Foreign Affairs on the pandemic threat.

According to a recent report by the Center for Infectious Disease Research and Policy, influenza pandemics are the greatest threat of a worldwide infectious disease crisis, and the world needs to be better prepared for the possibility of a pandemic.

Ten influenza pandemics have hit the world over the last 300 years, the two most recent were in 1957-58 and 1968-69, and although several tens of thousands of Americans died in each one, these were considered mild compared to previous ones.

In the 1918-19 pandemic recent analysis estimates that 50 to 100 million people were killed globally. With the present world population at 6.5 billion, more than three times that of 1918, even a "mild" pandemic could kill many millions of people.

Concern has been heightened in recent years of an impending pandemic due to a number of events and factors. H5N1, the avian influenza strain currently circulating in Asia is a major worry. At this point in time scientists are uncertain if, when or where a pandemic will hit.

Osterholm says that in reality a pandemic once underway cannot be avoided, and only its impact can be lessened and although some important preparations are being made, more needs to be done by institutions at many levels of society.

There are apparently three significant types of influenza virus, and influenza type A infects and kills the greatest number of people each year and is the only type that causes pandemics. It usually starts in wild aquatic birds and does not cause illness in these birds, and although it is widely transmitted among them, it does not undergo any significant genetic change.

To date, direct transmission from the birds to humans has not been proven, but when a virus is transmitted from wild birds to domesticated birds such as chickens, it undergoes changes that allow it to infect humans, pigs, and potentially other mammals. Once in the lung cells of a mammalian host, the virus can lead to an entirely new viral strain, capable of sustained human-to-human transmission. If such a virus has not circulated in humans before, the entire population will be susceptible and most people will lack immunity from previous infection.

If the novel strain better adapts to humans and is easily transmitted from person to person, it is capable of causing a new pandemic. As the virus passes repeatedly from one human to the next, it eventually becomes less virulent and joins the other influenza viruses that circulate the globe each year. This cycle continues until another new influenza virus emerges from wild birds and the process begins again.

Some pandemics result in much higher rates of infection and death than others. Scientists today understand that this variation is a result of the genetic makeup of each specific virus and the presence of certain virulence factors, which is why the 1918-19 pandemic killed many more people than either the 1957-58 or the 1968-69 pandemic.

The number one killer of humans worldwide is still infectious diseases. There are today more than 39 million people living with HIV, and last year about 2.9 million people died of AIDS, bringing the cumulative total of deaths from AIDS to approximately 25 million.

Tuberculosis (TB) and malaria also remain major causes of death.

In 2003, about 8.8 million people became infected with TB, and the disease killed more than 2 million. Each year, malaria causes more than 1 million deaths and close to 5 billion episodes of clinical illness. In addition, newly emerging infections, diarrheal and other vector-borne diseases, and agents resistant to antibiotics pose a serious and growing public health concern.

Therefore, should an influenza pandemic strike today, borders would close, the global economy would shut down, international vaccine supplies and health-care systems would be overwhelmed, and panic would reign. To limit the fallout, says Osterholm, the industrialized world must create a detailed response strategy involving the public and private sectors.