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On 11 June, the World Health Organization declared that infections with the new H1N1 strain of influenza A virus had reached pandemic proportions. By then, a team of scientists in Japan and the United States had already begun characterizing the swine-origin virus from samples isolated from five patients in the United States, the Netherlands and Japan. On page 1021, they detail the virus's replicative efficiency as well as its sensitivity to antiviral drugs. Yoshihiro Kawaoka, a virologist at the University of Tokyo's Institute for Medical Science, shares what he learned from early clinical accounts of H1N1.

Could 2010 see a 1918-style pandemic?

It is a concern, but it is very difficult to say whether a 1918-type outbreak will occur. There are similarities to the 1918 strain — both infect cells deep inside the lungs. And our work shows that only people over 90 years old who were exposed to the 1918 influenza pandemic have antibodies to this H1N1 virus. There is a common misconception that people over the age of 60 who were exposed to other swine-flu outbreaks have antibodies, but our data do not support this.

What do clinicians need to know about this virus?

Clinicians need to understand the prevalence of this virus. Any patient presenting with symptoms of a respiratory infection should be tested for swine-origin influenza. I know of one instance in which H1N1 swine-origin influenza was not suspected when a patient presented to their doctor and the virus then spread to other family members. That incident demonstrates that physicians should be on high alert because of the importance of early treatment with antiviral drugs.

Will the available drugs help against H1N1?

Yes, our data show that existing and experimental antiviral drugs, including Tamiflu and Relenza, effectively treat these strains of H1N1. However, developing countries do not have enough of these drugs. And it seems unlikely that there will be enough vaccine to protect all susceptible people, even though drug companies are producing as much as possible.

What can the average person do to prevent illness?

The best thing to do is avoid crowds. The worry is that sustained transmission between humans could lead to a more harmful strain. Right now, most infected patients will have mild symptoms, but a few will have severe illness. Everyone — even young people — should see a physician when they have flu symptoms.