Influenza has the potential to infect many people quickly. Although the death rate for seasonal flu is probably only around 1% of those affected, when the numbers so affected run into millions, as they do in India, the number of people who die will also be large. It is this potential that generates fear and underlies the near-hysteria that is now sweeping across western India and threatens to do so in the rest of the country over the spread of the A(H1N1) virus. (Editorial)