Epidemiology & Disease Prevention - Cerro Gordo County Department of Public Health

Disease Prevention

Pandemic Flu: Frequently Asked Questions FAQ Key

H5N1

Will the H5N1 bird flu virus cause the next influenza pandemic?
Scientists cannot predict whether an avian influenza (H5N1) virus will cause a pandemic. Today, H5N1 is a bird flu. There are no reported cases of sustained human-to-human passage of H5N1. However, as it mutates, it is possible the virus could become capable of passing human to human and then spread very quickly. That is why we are focusing on comprehensive public health efforts - increasing surveillance, monitoring for outbreaks, international cooperation, increasing antiviral stockpiles, and building more robust capacity for vaccine production - that will help protect us no matter what pandemic strain emerges or where.

What changes are needed for H5N1 or another avian influenza virus to cause a pandemic?
Three conditions must be met for a pandemic to start:

A new influenza virus subtype must emerge for which there is little or no human immunity
It must infect humans and cause illness
It must spread easily and continue without interruption among humans

The H5N1 virus in Asia, Europe, and Africa meets the first two conditions: it is a new virus for humans (H5N1 viruses have never circulated widely among people), and it has infected a growing number of people, killing over half of those known to have been infected. However, the third condition, the establishment of efficient and sustained human-to-human transmission of the virus, has not occurred. For this to take place, the H5N1 virus would need to improve its transmissibility among humans.

How does H5N1 virus differ from seasonal influenza viruses that infect humans?

Review this comparison chart

Unlike seasonal influenza, in which infection usually causes only mild respiratory symptoms in most people, H5N1 infection may follow an unusually aggressive clinical course, with rapid deterioration and high fatality. Primary viral pneumonia and multi-organ failure have been common among people who have become ill with H5N1 influenza.

Of the few avian influenza viruses that have crossed the species barrier to infect humans, H5N1 virus has caused the largest number of reported cases of severe disease and death in humans. In the current situation in Asia, Europe, and Africa, more than half of the people infected with the virus have died. Most cases have occurred in previously healthy children and young adults. However, it is possible that the only cases currently being reported are those in the most severely ill people and that the full range of illness caused by the H5N1 virus has not yet been defined.