What is the new influenza A(H1N1)?

This is a new influenza A(H1N1) virus that has never before circulated among humans. This virus is not related to previous or current human seasonal influenza viruses.

Why are we so worried about this flu when hundreds of thousands die every year from seasonal epidemics?

Seasonal influenza occurs every year and the viruses change each year - but many people have some immunity to the circulating virus which helps limit infections. Some countries also use seasonal influenza vaccines to reduce illness and deaths.

But influenza A(H1N1) is a new virus and one to which most people have no or little immunity and, therefore, this virus could cause more infections than are seen with seasonal flu. WHO is working closely with manufacturers to expedite the development of a safe and effective vaccine but it will be some months before it is available.

The new influenza A(H1N1) appears to be as contagious as seasonal influenza, and is spreading fast particularly among young people (from ages 10 to 45). The severity of the disease ranges from very mild symptoms to severe illnesses that can result in death. The majority of people who contract the virus experience the milder disease and recover without antiviral treatment or medical care. Of the more serious cases, more than half of hospitalized people had underlying health conditions or weak immune systems.

Most people experience mild illness and recover at home. When should someone seek medical care?

A person should seek medical care if they experience shortness of breath or difficulty breathing, or if a fever continues more than three days. For parents with a young child who is ill, seek medical care if a child has fast or labored breathing, continuing fever or convulsions (seizures).

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