Sometimes a new type of influeza virus appears that causes an illness that is more serious than is usually the case for flu. This happened, for example, in 1918, when a flu pandemic killed between 20 million and 100 million people. Recently, there have been concerns about the new type of bird (avian) flu. At present the virus responsible does not pass easily from birds to humans, and it does not seem to pass from one human to another. However, the fear is that the virus might change and that human-to-human infection could then be possible. Should all this happen, the changed virus would be a major threat to human health.

With current technology, it would take several months to produce enough vaccine against such a new virus for even a small proportion of the world's population. By that time, it would probably be too late; the virus would already have spread to most parts of the world.

Health authorities must therefore consider all the methods that might control the spread of the virus. With the increase in international travel that has taken place, the virus could spread more quickly than in previous pandemics. Restrictions on international travel might be considered necessary, particularly travel by air. However, it is important to estimate how useful restrictions on air travel might be in controlling the spread of a flu virus. Travel restrictions are usually unpopular and could themselves be harmful. If they are not effective, resources could be wasted on enforcing them.

Researchers of the Centre for Infections, Health Protection Agency, UK used the techniques of mathematical modelling. In other words, complex calculations were done using information that is already a
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Contact: Andrew Hyde
ahyde@plos.org
44-122-346-3330
Public Library of Science
1-May-2006