This article, published by the WHO, answers frequently asked questions about the A(H1N1) influenza virus, or 'swine flu'. It provides information on the availability, production and effectiveness of A(H1N1) vaccines.

The WHO says that no effective A(H1N1) vaccines are currently available (May 2009) but adds that work is underway to develop one. The Centers for Disease Control and Prevention in the United States, for example, has identified and prepared candidate vaccine strains and is distributing them to all interested parties on request.

A vaccine could be available in five to six months after a pandemic strain has been identified but the WHO notes that more than 90 per cent of the global capacity for vaccine production lies in Europe or the United States — which may have implications for vaccinating people in developing countries. While these countries are well-versed in distributing vaccines through mass campaigns, they may face difficulties in ensuring timely access to enough supplies of vaccine.

This article, published by the WHO, assesses the potential for a global pandemic of A(H1N1) influenza, or 'swine flu'. The authors outline the properties of influenza viruses that are needed to create a pandemic and discuss population vulnerability and pandemic severity. They highlight the populations at most risk, for example people with underlying conditions such as cardiovascular disease, and the role that nutritional status and the quality of health services can play in influencing a pandemic's severity.

In assessing the 2009 swine flu outbreak, they draw attention to the fact that mutations often occur in influenza viruses, which means that while the emerging virus may be mild, it could return in several months in a much more lethal form.

The authors say that A(H1N1) is a new influenza virus not previously seen in humans or animals. They suggest that it is more contagious than seasonal flu, but note that outside Mexico where the outbreak began, the virus is causing very mild illness in otherwise healthy people. They emphasise the risk to people suffering from other chronic diseases and note that the WHO estimates that 85 per cent of these people are in developing countries.

This timeline, published by Nature, lists key dates and events in the 2009 outbreak of A(H1N1) influenza, or 'swine flu'. Drawing on information from the WHO, the US Centers for Disease Control and Prevention and others, it details confirmed and reported cases of A(H1N1), highlights the geographical spread of the virus and links to official documentation and key research findings as they are released.

This fact sheet from the WHO outlines the basics about swine influenza, or "swine flu", including what it is, what its implications are for human health and how people become infected.

To protect yourself from swine flu, the WHO recommends avoiding contact with sick pigs or people, washing your hands regularly, practicing good health habits and following advice from local health authorities.