What Percentage Of People In Europe May Be Infected In Pandemics?

Featured Article
Main Category: Swine Flu
Also Included In: Flu / Cold / SARS;  Public Health;  Infectious Diseases / Bacteria / Viruses
Article Date: 03 May 2009 - 8:00 PDT

email to a friend   printer friendly   opinions  

For a pandemic to be a pandemic the virus needs to be a new influenza virus; therefore the majority of the population has no immunity to it, or very little immunity. We currently do not know what the level of immunity is to the swine flu virus among people in Europe. We are uncertain who the special higher risk groups might be.

Because a large number of people are infected in pandemic:

• some people will be asymptomatic (they will have no symptoms at all)
• several will have mild symptoms

Nevertheless, a small percentage of the people will experience more severe symptoms and will need to be hospitalized. Sadly, a small proportion of this small percentage will die prematurely, usually as a result of an influenza infection.

The best way to work out what these percentages might be is to look back to the experience of the pandemics that occurred in 1918, 1957, and 1968.

That is the foundation for planning assumptions published by WHO and several EU nations. What follows summarizes that information in a European context.

Below are examples of percentages of people who actually had symptoms - clinical attack rates. The percentages refer to the whole population. As many infected people have no symptoms, a 50% attack rate would mean an infection rate of approximately 85%.

Examples of clinical attack rates from previous pandemics:

• New York State (1918) - 35%
• Manchester (1918) - 25%
• Leicester (1918) - 30%
• Warrington & Wirral (1918) - 23%
• South East London (1957) - 32%
• Kansas City (1957) - 34%
• Kansas City (1968) - 39%

A typical clinical attack rate of 25% to 35% means an approximate 50% infection rate if one includes those people who had no symptoms.

What percentage of patients would benefit from hospitalization because of influenza?

Generally, about 4% of those who become ill would benefit from hospitalization. However, some patients are more likely to benefit than others - those in the so called high risk groups.

What fatality rates were reported in previous pandemics?

• Spanish flu (1918-1919) 2-3 %
• Asian flu (1957-1958) < 0.2 %
• Hong Kong (1967-1968) < 0.2%

The European Centre for Disease Prevention and Control says that work is being carried out to estimate these types of data for an existing outbreak. An estimate will take some time to complete.

The European Centre for Disease Prevention and Control says the most useful information is currently coming from the USA, rather than Mexico, as Mexico has been focusing more on the severe cases which does not give a true overall picture.

Planning assumptions

Several countries have utilized this data to make planning assumptions for pandemics. The European Centre for Disease Prevention and Control held a meeting of these groups in 2008. The data came from that meeting. The planning assumptions tend to represent the worst that a local area expert may expect - because that possibility has to be planned for.

Source
European Centre for Disease Prevention and Control

• See our Map Of H1N1 Outbreaks
• See our Mexico Swine Flu Blog

Written by - Christian Nordqvist
Copyright: Medical News Today
Not to be reproduced without permission of Medical News Today

• Additional
• References
• Citations