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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: 1) a new influenza virus subtype must emerge; 2) it must infect humans and causes serious illness; and 3) it must spread easily and sustainedly (continue without interruption) among humans. The H5N1 virus in Asia and Europe meets the first two conditions: it is a new virus for humans (H5N1 viruses have never circulated widely among people), and it has infected more than 100 humans, killing over half of them.
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 have to change in such a way that it could spread more easily among humans. This could occur either by “reassortment” or adaptive mutation.
Reassortment occurs when genetic material is exchanged between human and avian viruses during co-infection (infection with both viruses at the same time) of a human or pig. The result could be a fully transmissible pandemic virus—that is, a virus that can spread easily and directly to humans. A more gradual process is adaptive mutation, where the capability of a virus to bind to human cells increases during infections of humans.
What is CDC doing to prepare for a possible H5N1 influenza pandemic?
CDC is taking part in a number of pandemic prevention and preparedness activities, including the following:
- Providing leadership to the National Pandemic Influenza Preparedness and Response Task Force, created in May 2005 by the Secretary of the U.S. Department of Health and Human Services.
- Working with the Association of Public Health Laboratories on training workshops for state laboratories on the use of special laboratory (molecular) techniques to identify H5 viruses.
- Working with the Council of State and Territorial Epidemiologists and others to help states with their pandemic planning efforts.
- Working with other agencies, such as the Department of Defense and the Veterans Administration, on antiviral stockpile issues.
- Working with the World Health Organization (WHO) to investigate influenza H5N1 among people (e.g., in Vietnam) and to provide help in laboratory diagnostics and training to local authorities.
- Performing laboratory testing of H5N1 viruses.
- Starting a $5.5 million initiative to improve influenza surveillance in Asia.
- Holding or taking part in training sessions to improve local capacities to conduct surveillance for possible human cases of H5N1 and to detect influenza A H5 viruses by using laboratory techniques.
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- Developing and distributing reagent kits to detect the currently circulating influenza A H5N1 viruses.
CDC also is working closely with the World Health Organization and the National Institutes of Health on safety testing of vaccine candidates and development of additional vaccine virus seed candidates for influenza A (H5N1) and other subtypes of influenza A viruses.
What can my family do to prepare for a possible influenza pandemic?
One of the most important protective steps against a possible influenza pandemic is avoiding infection. For the most part, ordinary measures, such as hand hygiene and remaining several feet away from people who show symptoms of respiratory illness (e.g., coughing, sneezing), could be useful protection strategies.
What can businesses do to prepare for a possible influenza pandemic?
Businesses should stay informed about the potential for an influenza pandemic. They should develop or update emergency plans and consider in advance the challenges they could face if an influenza pandemic occurred. Businesses should identify essential functions and personnel needed to keep the business operating and should work with medical advisors on ways to protect employees.
What can communities do to prepare for a possible influenza pandemic?
Communities should carefully review the resources they have in place. They may need to build upon existing emergency plans in preparation for a possible influenza pandemic. For instance, communities can identify possible communication barriers (e.g., diverse languages) and other possible barriers to effective medical care. They also can develop a list of resources and plan for groups that might be hardest hit during an influenza pandemic.
Communities should coordinate their plans with state and federal influenza pandemic plans. They should test their plans regularly and change them as needed to improve response in case of an influenza pandemic.
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