The US Centers for Disease Control (CDC) describes a pandemic as the outbreak of a global disease. A flu pandemic can happen when a new influenza virus develops for which people have little or no immunity, and there is no vaccine. The disease easily spreads from person-to-person, causes serious illness, and can move across the country and around the world rapidly. No one can easily predict when the next flu pandemic will occur or its severity. However, once it starts, everyone is at risk. Measures such as border closures and travel restrictions, might delay transmittal of the virus, but will not stop it.
Health experts are concerned about the continued spread of a highly pathogenic avian H5N1 virus across eastern Asia and elsewhere. This virus may be a significant threat to human health. The H5N1 virus increases concerns about a potential human pandemic because for these reasons: it is very infectious, it is spread by migratory birds, it can be transmitted from birds to mammals and in some circumstances to humans, and it continues to evolve.
Avian influenza is generally a low risk to most people, because these viruses do not usually infect humans. However, H5N1 has crossed the species barrier to infect humans, and it is quite deadly. Most cases of the infection in humans have occurred from contact with infected poultry or surfaces contaminated with fluids from infected birds. To date, the spread of H5N1 virus from person to person has been limited. Because all influenza viruses can mutate, scientists are concerned that H5N1 virus could be able to infect humans and spread easily from one person to another.
If an especially severe influenza pandemic were to occur, it could lead to high levels of illness, death, social disruption, and economic loss. Everyday life would be seriously disrupted as many people became seriously ill simultaneously. The results could range from school and business closings to interruptions of basic services such as public transportation and food delivery. A substantial percentage of the population will require medical care in some form. Health care facilities could be overwhelmed, with shortages in hospital staff, beds, ventilators, and supplies. Additional capacity at sites such as schools may need to be created to handle the demand.
For a pandemic to begin, three conditions need to be present: 1) a new influenza virus subtype must develop for which people are not immune; 2) the virus must cause illness in humans; and 3) it must spread easily and continue spreading among humans. The H5N1 virus in Asia, Europe, and Africa meets the first two conditions and has killed over half of those whom it has infected. The third condition, sustained human-to-human transmission of the virus, has not happened.
The avian flu is highly contagious and yet there are no symptoms for two days after contact. Absentee rates in the workforce could be 30 percent or higher as employees are either sick, caring for a family member, or afraid to come to work. According to CDC estimates, a moderate flu outbreak would cause between 88,000 and 300,000 deaths; a severe outbreak could cause 1.8 million deaths. (The seasonal flu causes about 36,000 deaths per year). It will come in waves lasting from 4 to 12 weeks and continue for one to two years. A vaccine will not be ready during the initial wave as it could take up to six months to isolate the strain and start production. Current anti-viral drugs are not effective against it. The drugs Tamiflu and Relenza, which may or may not work, are in short supply.
The World Health Organization (WHO) has identified five phases leading up to the pandemic (which is Phase 6). The phases are 1) the "inter-pandemic" phase, the period between pandemics; 2) a new virus infects animals, but not, as yet, human beings; 3) human beings are infected, but almost never by other people; 4) evidence of increased human-to-human transmission; 5) the clusters of infected cases which formed during Phase 4 become larger and more numerous; and 6) the virus is transmitted by human beings to one another in an efficient and sustained way: the pandemic—Phase 6—has begun.
We are currently in Phase 3, says the director-general of the WHO.