Flu Pandemics
A flu pandemic (or worldwide epidemic) occurs when a new flu virus, to which people have little or no immunity, emerges and starts to spread.1 There were three flu pandemics in the last century (1918-1919, 1957 and 1968) and so far, there has been one in this century (2009-10).1 The 1918-19 pandemic was the most severe with 40-50 million deaths worldwide.1
The 2009-10 pandemic, the first for 40 years, was caused by the influenza A(H1N1)v strain (commonly known as swine flu in the UK).1 Although the pandemic has ended, the strain continues to circulate and cause disease in many countries. The World Health Organization (WHO) recommended it to be included in the 2011/12 seasonal flu vaccine.2
What’s the difference between seasonal flu and pandemic flu?3
| Seasonal Flu | Pandemic Flu | |
| When does it occur? | Every year in winter | Any time of the year |
| Who does it affect? | Up to 10% of the population | Up to 25% of the population |
| Who is most at risk of serious illness? | The very young, the very old and people with certain chronic illnesses | People of any age |
Because the strain that causes a pandemic can’t be predicted, vaccines to prevent it can’t currently be
manufactured until the specific virus strain has begun to circulate.1
1. Department of Health. Immunisation against infectious diseases – The Green Book. Chapter 23a Pandemic influenza A(H1N1)v 2009.
2. WHO. Recommended viruses for use in the 2010-2011 northern hemisphere influenza season. http://www.who.int/entity/csr/disease/influenza/201002_Recommendation.pdf. Accessed 30/03/2011.
3. NHS Leaflet. Pandemic Flu – Important Information for you and your family. October 2005.