What Is a Pandemic (Influenza)?

Featured Article
Main Category: Flu / Cold / SARS
Also Included In: Immune System / Vaccines;  Swine Flu
Article Date: 25 Sep 2005 - 16:00 PDT

email to a friend   printer friendly   opinions  

A pandemic is of global proportions, an influenza pandemic occurs when the influenza (type A) virus surfaces in the human population. An influenza pandemic causes serious and often fatal illness and spreads rapidly from human-to-human.

An epidemic, as opposed to a pandemic, tends to be seasonal and does not cover such a large geographical area. An influenza epidemic occurs when an already existing subtype of the flu virus spreads.

An influenza pandemic, on the other hand, occurs when a new subtype(s) emerges among the human population. This new subtype(s) has never spread from human-to-human before.

In everyday English the difference between Pandemic and Epidemic is becoming quite clear - a Pandemic is global and an Epidemic is not.

Flu viruses come as many subtypes. They differ according to proteins present on their surface. Two main proteins help us identify the subtypes - the HA (hemagglutinin) and NA (neuraminidase) proteins.

Pandemics tend to occur when an influenza A virus undergoes an 'antigenic shift'. The combinations of NA and HA proteins on the surface of the virus change and a new influenza virus subtype is born. If this new subtype can spread easily from human to human, then the chances of a pandemic occurring increase greatly.

In the last century there were three influenza A virus pandemics. They all became global within twelve months:

- Spanish Flu. 1918 - 1919.

The virus was known as A H1N1. Over half a million Americans died. Estimates put the global death toll at 50 million people. Half of those fatalities were among young healthy people.

- Asian Flu 1957 -1958

The virus was known as A H2N2. About 70,000 Americans died, millions died worldwide.

- Hong Kong flu 1968 - 1969

This virus was known as A H3N1. 34,000 Americans died.

The last two pandemics contained genes from a human influenza virus and an avian (bird) influenza virus.

The present Pandemic threat comes from the bird flu virus, called H5N1. At the moment it only spreads from birds to humans. There is, as yet, no evidence that it can spread from human-to-human. There have been cases this year of people caring for infected patients or relatives becoming infected (but they did not go on to infect others). However, as is often the case with a virus, it can mutate. Many experts believe the easiest route for the H5N1 to mutate and become a pandemic threat to humans is if it evolves in a pig. If it evolved within a pig, and from the pig infected a human, the chances of it being a human-to-human transmissible virus are much greater.

At present, there is no vaccine against a possible bird flu threat. It is difficult to make a vaccine if you cannot predict accurately what the new evolved virus is going to be like. Many people are taking the normal flu vaccine in the hope that this will give them 'some' measure of protection. But the reality is that nobody knows.

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

• Additional
• References
• Citations