Every so often, perhaps at 10 or more year intervals, the virus may undergo a major change and antibodies from previous infections or immunisation with vaccine will be totally ineffective.

The virus is usually named from the year and location of the laboratory where it is first isolated.

The great influenza pandemic of 1918-1919 was thought to be due to a strain commonly called “swine flu” because it occurs in pigs as well as man.

The New Jersey strain, first noted when a small outbreak occurred at an army camp, Fort Dix, in New Jersey caused health authorities a lot of worry for it appeared to be the same “swine flu” which caused widespread infection just after World War I.

Fearing another pandemic, the U.S. Government mounted a mass immunisation campaign.

More than 50 million people were immunised and the outbreak was confined to a small area. The feared epidemic did not eventuate.

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