What's the difference between ordinary flu and pandemic flu?

Pandemic flu occurs when a new, highly infectious and dangerous strain of the flu virus appears. Because it's so different to other strains of flu, we have little or no immunity to it, and it can spread easily, from person to person, and from country to country.

Ordinary flu happens every year usually during the winter, whereas pandemic flu tends to occur only three times each century. Ordinary flu has unpleasant symptoms such as headaches, sore throat, cough, aching muscles and fever, but in most cases is not life threatening. Pandemic flu has similar symptoms, but they are much more severe, and can be life threatening.

An annual vaccine for ordinary flu is available to those most at risk from complications such as bronchitis, including the over 65s and people with long-term conditions like asthma. However, there is no vaccine available for pandemic flu because it's not possible to predict the strain of the virus. If a pandemic occurs, scientists should be able to develop a vaccine within a few months.