From Anna Spector,
Your Guide to Infectious Diseases.
FREE Newsletter. Sign Up Now!

About.com Health's Disease and Condition content is reviewed by Susan Olender, MD

A. Predicting the number of deaths of a possible pandemic flu involves looking at past pandemics as well as estimating the response we can provide for a pandemic today.

How does the World Health Organization (WHO) estimate a loss of only 2-7.4 million lives to a pandemic flu if it were to happen today? It turns out that the calculation is based upon the relatively mild pandemic of 1968. This is somewhat controversial since it is thought that perhaps the 1968 epidemic was milder than previous ones because it came only nine years after the last one. Perhaps people had some immunity to the 1968 H3N2 virus because it shared the same type of neuraminidase (N) as the 1957 H2N2 virus.

In the 1918 Spanish Flu pandemic caused by the avian flu virus H1N1, killed 40-50 million people, and by some estimates up to 100 million. The world's population was around 1.6 billion people in 1910 according to the census available, so if the H1N1 virus killed 40 million (a low figure) then that would be around 0.025 per cent of the total population. Today's global population is around 6 billion. If a pandemic flu killed 0.025 per cent of the population, that would amount to 150 million people. So why doesn't the WHO predict a death toll of 150 million people?

It turns out, that many people die, not from flu itself, but from complications of the flu, such as pneumonia, many of which can be treated with antibiotics that did not exist in 1918. The 1918 flu is considered an exception, not your usual pandemic. The last two pandemics, in 1957 and 1968, killed 1-2 and less than one million people respectively, and it is assumed that one reason for the decline in deaths over the 1918 pandemic was the availability of antibiotics, better nutrition, and better management of complications.

In general, mortality is determined by four factors, according to information on the pandemicflu.gov website.

1. The number of people infected by the virus.
2. The severity of the virus (ability to cause severe illness and death).
3. The situation and circumstances of the people infected. These could include nutritional state, age (the population is aging), immunity (high risk groups are likely to be people with immune disorders such as HIV/AIDS).
4. The measures taken to prevent and treat the disease. This includes drug availability such as anti-virals and antibiotics to combat complications and vaccines to prevent disease.

In summary, no one really knows how many people would die in the next pandemic.

Sources:

• The World Almanac and Book of Facts. Nations, World Area and Populations. 2002.
• Taubenberger JK, Moren DM. 1918 Influenza: The Mother of All Pandemics. Emerg Infect Dis. Serial on the Internet. Jan 2006. See text at http://www.cdc.gov/ncidod/EID/vol12no01/05-0979.htm#cit
• World Health Organization. Assessing the pandemic threat. January 2005. See text http://www.cdc.gov/ncidod/EID/vol12no01/05-0979.htm#cit
• Kilbourne ED. Influenza pandemics of the 20th century. Emerg Infect Dis. Jan 2006. See text http://www.cdc.gov/ncidod/EID/vol12no01/05-1254.htm#cit
• US Government. Pandemic Flu Website. General Information. See text http://www.pandemicflu.gov/general/#impact
• Luke CJ, Subbarao K. Vaccines for pandemic influenza. Emerg Infect Dis. Jan 2006. See text http://www.cdc.gov/ncidod/EID/vol12no01/05-1147.htm#cit