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What is Influenza?

Each year, ordinary seasonal influenza or flu affects many thousands of people in the UK and millions worldwide, producing symptoms ranging from those similar to a common cold through to very severe symptoms or even death.

Flu is a virus that can infect the lungs and airways of humans and some animals, such as birds and pigs. It is typically spread through the air by coughs and sneezes, or direct contact with secretions from the nose and contaminated surfaces.

Flu viruses constantly change and mutate. Small changes in proteins called antigens on the outer surface of the virus happen over time and during transmission of the virus from person-to-person. This causes the changes to seasonal flu that require us to get vaccinated each year.

By contrast, pandemic influenza strains can arise from major antigen changes, for example when a human and animal flu strain combine. In such cases there is little or no immunity to this new virus in the population and large numbers of people can become infected in a short space of time. 

Why do we need research into early warning sensing systems for influenza?

Early detection of influenza outbreaks plays a crucial role in pandemic emergency response strategies.

Over the last century four pandemics have occurred, each by the emergence of a new strain of the virus never before seen in humans, killing tens of millions of people. For example, the 1918 Spanish flu pandemic killed an estimated 20 to 50 million people, mostly young adults. The economic impact was estimated to be between 16.9 and 2.4 per cent of GDP.1 

The emergence of H5N1, commonly called ‘bird flu’ in South-east Asia, the 2009 H1N1 ‘swine flu’ outbreak in Mexico, and the 2013 H7N9 strain of swine flu in China, highlight that new strains could emerge at any time, in any part of the world and can pose a pandemic threat.

Early detection of both seasonal and pandemic strains plays a crucial role in pandemic preparedness. However, influenza largely remains undetected and undiagnosed, resulting in a significant, but not well understood burden of disease. This is important to understand, as it helps inform the use of interventions, such as vaccination. 

A recently published, five year study compared the burden and severity of seasonal and pandemic influenza in England2. The study, led by Professor Andrew Hayward and published in Lancet Respiratory Medicine, found that around one in five of unvaccinated persons were infected each season due to seasonal flu. However, just 23 per cent of these infections were estimated to cause symptoms, and only 17 per cent of laboratory-confirmed cases resulted in the person visiting their doctor. A similar picture was seen with the 2009 H1N1 influenza pandemic.

The ability to rapidly measure such information offers important lessons for future pandemic preparedness strategies. Early detection and assessment of pandemic severity is key to ensure public health efforts are optimally deployed to protect populations.

Related links


UK Influenza Pandemic Preparedness Strategy 2011 

2 Hayward, A.C, et al. Comparative community burden and severity of seasonal and pandemic influenza: results of the Flu Watch cohort study. The Lancet Respiratory Medicine, 2, 445 - 454 (2014), DOI: 10.1016/S2213-2600(14)70034-7