What is the difference between ordinary influenza and pandemic influenza?
Ordinary influenza is the influenza that circulates most of the time and produces the outbreaks we see in Canada every winter. For most people this is an unpleasant though not life-threatening illness. The strains of virus causing this type of influenza change from year to year, but can be fairly reliably predicted so that an appropriate vaccine can be prepared each year. Pandemic influenza is caused when a new strain of influenza virus emerges that is markedly different from recently circulating strains. These changes cannot be predicted in the same way as the changes in ordinary influenza viruses, so a vaccine specifically against the new strain cannot be developed in advance.
