What is an influenza pandemic?

A pandemic is a global disease outbreak. An influenza pandemic occurs when a new influenza A virus emerges for which there is little or no immunity in the human population, begins to cause serious illness and then spreads easily person-to-person worldwide.

How do pandemic viruses occur?

New influenza viruses emerge as a result of a sudden and major change in influenza A viruses. These changes occur when proteins on the surface of the virus combine in new ways as a result of mutation or exchange of genetic material between multiple influenza viruses. If such changes result in a new influenza A virus subtype that can infect humans and spread easily from person to person, an influenza pandemic can occur.

Is a pandemic imminent?

Scientists agree it is a matter of time until the next influenza pandemic occurs. However, the timing cannot be predicted. Influenza pandemics occurred three times in the past century — in 1918-19, 1957-58, and 1968-69, causing enormous numbers of deaths and illnesses.

The H5N1 virus has raised concerns about a potential human pandemic because:
  • The H5N1 virus is widespread in poultry in many countries in Asia and Europe;
  • The virus has been transmitted from birds to mammals and in some cases to humans;
  • Wild birds and domestic ducks have been infected without showing symptoms and become carriers of viral infection to other domestic poultry species;
  • Genetic studies confirm that H5N1 influenza viruses, like other influenza viruses, are continuing to evolve.
Why won't the annual flu vaccine protect people against pandemic influenza?

Influenza vaccines are designed to protect against a specific virus, so a pandemic vaccine cannot be produced until a new pandemic influenza virus emerges and is identified. Even after a pandemic influenza virus has been identified, it could take at least 6 months to develop, test and produce vaccine.

How much time does it take to develop and produce an influenza vaccine?

The influenza vaccine production process is long and complicated. Traditional influenza vaccine production relies on technology based on chicken eggs. This production technology is labor-intensive and takes 9 months from start to finish. The flu vaccine production process is further complicated by the fact that influenza virus strains continually evolve. Thus, seasonal flu vaccines must be modified each year to match the strains of the virus that are known to be in circulation among humans around the world. As a result of this constant viral evolution, seasonal influenza vaccines cannot be stockpiled year to year. Researchers are making and testing possible H5N1 vaccines now. However, large amounts of vaccine cannot be made before knowing exactly which virus will cause the pandemic. It could then take up to 6 months before a vaccine is available.