Explaining Pandemic Flu: A Guide from the Chief Medical Officer

This guide aims to provide professionals and members of the public with a better understanding of pandemic influenza (flu), its likely impact on the United Kingdom (UK) and the country's plans to respond.

The publication begins by explaining the nature of influenza. Flu is an illness resulting from infection by an influenza virus. It is highly infectious and can spread easily from person to person. Because the flu virus constantly changes there are many different strains of flu. Some are more infectious and cause more severe illness than others. These changes can be minor - known as antigenic drift - or major, known as antigenic shift. These changes mean that few people have immunity to the flu, and it can spread very quickly, with more acute illness. Epidemics of ‘ordinary’ flu occur every year around the world. A pandemic, on the other hand, spreads around the world affecting many hundreds of thousands of people across many countries.

The publication also explains how avian influenza (also known as avian flu or bird flu) is a contagious disease normally found in birds caused by a type of influenza virus. Domestic poultry flocks are especially vulnerable. Avian flu viruses do not normally infect species other than birds or pigs. Historically, human infections with avian influenza viruses have been rare and usually mild. However, since 1997 there have been several outbreaks of human infection.

Experts fear that the A/H5N1 avian influenza virus could trigger the next pandemic for several reasons. Firstly, it has already demonstrated an ability to infect people and cause severe disease - one of the key characteristics of a pandemic strain. Secondly, this particular virus has a documented ability to mutate and to acquire genes from viruses infecting other species. Experts fear that the virus could, either adapt, giving it greater affinity for humans, or exchange genes with a human flu virus, thereby producing a completely novel virus capable of spreading easily between people, and causing a pandemic.

The publication states that it is unlikely that the global spread of a pandemic flu virus could be prevented once it emerges. The emphasis in pandemic flu control is, therefore, on reducing its impact. Several tools help achieve this aim: year-round global surveillance; effective and accurate methods of diagnosis; vaccines (once they become available); antiviral drugs; and social interventions.

In the UK, a national pandemic influenza contingency plan is in place outlining actions to be taken in the event of a pandemic.