Q: I heard in the news that doctors in Turkey are reporting what appears to be an outbreak of avian flu in humans there. Although the actual virus remains to be confirmed, the avain flu virus appears to be spreading well past its initial area of outbreak despite efforts of world health officials. Is this an initial warning sign that we may indeed be heading towards a pandemic flu this year or next year? Tom Skoko, Miami, Florida
Kanta Subbarao: The avian H5N1 virus has clearly spread beyond the initial area of the outbreak in Southeast Asia. The virus is believed to have been spread by migratory birds. It is impossible to predict whether the outbreak will continue to spread and lead to a pandemic, but there is a risk of this happening and the situation is being monitored closely by public health officials.
Q: I have been following the story of bird flu in the media but haven't yet heard an explanation of what caused the 1918 bird flu to finally stop spreading and causing illness and death. Why didn't the virus gradually kill everybody, and how did it disappear? Could the current bird flu strain die off in the same way? Ahmad Sabir, Baton Rouge, Louisiana
Subbarao: The attack rate of the 1918 flu was very high, and a large part of the population became infected and many millions died. However, a majority of infected persons recovered from influenza and were immune to the virus. The virus was spread from person to person and could only infect susceptible people. Over time, the number of susceptibles in the population decreased—referred to as "herd immunity"—and the epidemic ended. The virus continued to infect people in annual seasonal epidemics until 1957.
Q: What do you think is the most serious health threat our planet faces heading into the future? Anonymous, New York, New York
Subbarao: The short-term health threats are infectious diseases that have been with us for a long time but are not well-controlled, such as malaria and tuberculosis, as well as other diseases that are new and unpredictable, such as those that are transmitted from animal species, including influenza. The longer-term health threats are cardiovascular disease and cancer.
Q: For seasonal flu, an effective vaccine is one that prevents illness, therefore a close genetic match is required between vaccine strain and circulating strain. With H5N1, since the virus is so often lethal, would it not make sense to redefine vaccine success as reducing risk of death rather than preventing illness? By this definition, we could begin making and distributing vaccine now rather than waiting for the pandemic strain to emerge.
Also, it appears in mice that killed mucosal vaccines have greater potential to protect against cross-strains than injected vaccines. What work is being done on mucosal vaccines for H5N1—killed or attenuated (I know of a flu-mist trial in Baltimore)? Anonymous, Gilroy, California
Subbarao: You are correct. A more realistic goal in the event of a pandemic may be to reduce the risk of severe illness and death rather than preventing infection. A strategy of preemptive vaccination against potential pandemic influenza is being discussed.
My laboratory at the NIH is working in collaboration with MedImmune Vaccines to develop and evaluate candidate live attenuated vaccines for pandemic influenza that will be delivered as a nasal spray or nose drops and will elicit a mucosal immune response.
Q: I am a high school teacher, and in the past several years we have hatched chickens as a class project with our embryology unit. Should I keep up this practice? The students in the past have always played with the baby chicks in class. Should I have any concerns? I get the fertilized eggs from a local farmer. Anonymous, Spring Valley High School, Huntington, West Virginia
Subbarao: It is probably okay as long as the farms are not reporting illness in the poultry, and the chicks are kept away from other avian species. Young chicks are susceptible to avian influenza, and they should not be handled by the children if the birds appear sick or have yellow diarrhea.
Q: If a human can be infected by contact with the virus from an infected chicken, as news reports indicate in Turkey, what exactly prevents a human from being infected by contact with an infected human? It is said it is spread from the gut of the bird, so is it not spread from the human gut? David Rothstein, M.D., Chicago, Illinois
Subbarao: There have been some rare incidents where people have probably been infected through close contact with an infected person, but there have not been any examples of sustained chains of person-to-person transmission of the H5N1 virus. We don't fully understand what properties enable an influenza virus to spread efficiently from person to person. The virus replicates primarily in the gastrointestinal tract of birds and in the respiratory tract of humans. We don't have clear evidence that the virus is present in large amounts in the gastrointestinal tract of people infected with H5N1, and we have no evidence of spread from this part of the human body.
Q: I will soon be traveling in several Asian countries where bird flu is prevalent. What precautions should I take as a traveler to protect myself? I am unlikely to be in close contact with live birds, but is it safe to eat poultry? Josie Goodman, Los Angeles, California
Subbarao: Well-cooked poultry should not pose a risk. The Centers for Disease Control and Prevention and World Health Organization Web sites post specific information for travelers. For more information, see
Q: I am a high school student and I want to become a public health official. Is there any particular plan of study you would suggest for me in college or graduate school? Also, what are the most interesting areas of public health administration at the moment in your opinion—AIDS, poverty, TB? Laurel, Indianapolis, Indiana
Subbarao: The usual route is to enroll in a master's in public health—or doctorate in public health—course after obtaining an undergraduate degree or after graduation from medical school. Selecting a particular area of public health administration to focus on is really dependent on your specific interests.