Wednesday, December 7, 2005
An influenza virus strain capable of causing the next human influenza pandemic could emerge with little or no warning in almost any part of the world. Three influenza pandemics occurred in the 20th century,
Wednesday, December 7, 2005
An influenza virus strain capable of causing the next human influenza pandemic could emerge with little or no warning in almost any part of the world. Three influenza pandemics occurred in the 20th century, in 1918, 1957, and 1968. The pandemics of 1957 and 1968 were serious infectious disease events that killed approximately two million and 700,000 people worldwide, respectively. The 1918-1919 pandemic, however, was catastrophic: it is estimated that it killed more than 500,000 people in the United States and more than 40 million people worldwide. The possibility that a new influenza virus could emerge to cause a similar pandemic among human beings is a very real threat for which we must prepare.
Of known influenza viruses, the highly pathogenic avian influenza (HPAI) H5N1 avian influenza virus that is spreading in domestic and migratory birds in Asia and most recently in Eastern Europe currently is of greatest concern. The HPAI H5N1 virus is primarily an animal pathogen that has, however, infected more than 130 people in Asia. Approximately half of the people diagnosed with H5N1 avian influenza infection have died. At this point in time, the virus has not yet demonstrated the ability to spread efficiently from animals to humans and is very inefficient in spreading person-to-person. Because the virus is now widespread in many bird species in several countries in Asia and likely elsewhere, eradication is probably not feasible. The feared human pandemic could become a reality if the H5N1 virus mutates further, remains highly virulent, and acquires the capability to spread as efficiently from person to person as do the commonly circulating virus strains that produce seasonal influenza epidemics. Even if H5N1 does not evolve into a pandemic strain, the possibility that a human influenza pandemic will occur at some time in the future is real.
On November 1, 2005, the President announced the National Strategy for Pandemic Influenza, and the next day U.S. Department of Health and Human Services (HHS) Secretary Michael O. Leavitt released an integral component of the National Strategy, the HHS Pandemic Influenza Preparedness and Response Plan. Together, these two documents provide a blueprint for a coordinated national strategy to prepare for and respond to a human influenza pandemic. The National Institutes of Health (NIH) within HHS, and the HHS/NIH National Institute of Allergy and Infectious Diseases (NIAID), in particular, have the primary responsibilities for conducting scientific research and clinical trials to foster product development to prepare our nation for a potential human influenza pandemic.
In my testimony today, I will tell you more about the scientific research and development efforts of the Federal Government, the academic community, and the private sector to counter the threat of pandemic influenza. In particular, I will focus on projects and programs that will help ensure that effective influenza vaccines and antiviral drugs will be available to counter any human influenza virus with pandemic potential that could emerge.
Basic Science and Surveillance
Each year, as influenza viruses circulate through the human population, their surface proteins undergo small changes. As these small changes accumulate, the influenza virus gains the ability to circumvent immunity created by prior exposure to older circulating influenza viruses or by vaccination. This phenomenon, called “antigenic drift,” is the basis for the well-recognized patterns of human influenza disease that occur predictably every year, and is the reason that, working with the World Health Organization (WHO), we must update influenza vaccines each year. Influenza viruses also can change more dramatically. For example, viruses sometimes emerge that can jump species from natural reservoirs, such as wild ducks, to infect domestic poultry, farm animals, or humans. When an influenza virus jumps species from an animal, such as a chicken, to infect a human, the result is usually a “dead-end” infection that cannot readily spread further in the human population. However, mutations in the virus could develop that allow human-to-human transmission. Furthermore, if an avian influenza virus and another human influenza virus were to simultaneously co-infect a person or animal, the two viruses might swap genes, possibly resulting in a virus that is readily transmissible between humans, and against which the population would have no natural immunity. These types of significant changes in influenza viruses are referred to as “antigenic shift.”
H5N1 and H9N2 are two avian influenza strains that have jumped directly from birds to humans. In 1998, 1999 and 2003, H9N2 influenza caused illness in three people in Hong Kong and in five individuals elsewhere in China, but the virus did not spread further among humans, and caused no known deaths. At this time, H5N1 influenza appears to be a significantly greater threat than H9N2. In addition to the