For healthy individuals, the flu is typically a moderately severe illness, with most adults and children back to work or school within a week. For the very young, the very old, and people who are not in good general health, however, the flu can be very severe and even fatal. Complications such as secondary bacterial infections may develop, taking advantage of the body's weakened condition and lowered resistance. The most common bacterial complication is pneumonia, but sinuses, bronchi (lung tubes), or inner ears also can become secondarily infected with bacteria. Less common but very serious complications include viral pneumonia, encephalitis (inflammation of the brain), acute renal (kidney) failure, and nervous system disorders. These complications can be fatal.
Who Gets the Flu?
Anyone can get the flu, especially if there is an epidemic in the community. (An epidemic is a period when the number of cases of a disease exceeds the number expected based on past experience.) During an epidemic year, 20-30% of the population may contract influenza. Not surprisingly, people who are not healthy are considered at high risk for most strains of influenza and their complications. The high-risk population includes those who have chronic lung conditions, such as asthma, emphysema, chronic bronchitis, tuberculosis, or cystic fibrosis; those with heart disease, chronic kidney disease, diabetes, or severe anemia; people residing in nursing homes; those older than age sixty-five years; and some health care workers.
Vaccines
Influenza can be prevented by inoculation with a current influenza vaccine, which is formulated annually so that it contains the influenza viruses expected to cause the flu the next year. The viruses are killed or inactivated to prevent those who are vaccinated from getting influenza from the vaccine. After being immunized, the person develops antibodies to the influenza viruses. The antibodies are most effective after one or two months. High-risk people should be vaccinated early in the fall because peak flu activity usually occurs around the beginning of the new calendar year. The flu season usually runs from October to May and peaks in December and January.
Each year's flu vaccine protects against only the viruses that were included in its formulation. If another strain of flu appears, people still can catch the new strain although they were vaccinated for the primary expected strains. The 2003–04 flu season was one of the worst in recent memories, with a nationwide shortage of vaccine early in the season, a time when the virus was peaking, and children were dying from the illness (at least 142 individuals under eighteen years old).
Most people have little or no noticeable reaction to the vaccine; 25% may have a swollen, red, tender area where the vaccination was injected. Children may suffer a slight fever for twenty-four hours or have chills or a headache. Those who already suffer from a respiratory disease may experience worsened symptoms. Usually, these reactions are temporary. Because the egg in which the virus is grown cannot be completely extracted, people with egg protein allergies should consult their physicians before receiving the vaccine and, if vaccinated, should be closely observed for any indications of an allergic reaction.
Pandemic Influenza
In "Pandemic Flu: Key Facts" the CDC defines pandemic flu as "a global outbreak of disease that occurs when a new influenza A virus 'emerges' in the human population, causes serious illness, and then spreads easily from person to person worldwide" (http://www.cdc.gov/flu/pandemic/pdf/pandemicflufacts.pdf). Pandemics are different from seasonal outbreaks or even epidemics of influenza. Seasonal outbreaks are caused by influenza viruses that already move from person to person, while pandemics are caused by new viruses, subtypes of viruses that have never passed between people, or subtypes that have not circulated among people for a very long time.
In the past, influenza pandemics have produced high levels of illness, death, social disruption, and economic loss. The twentieth century saw three pandemics. The CDC reports that the 1918–19 "Spanish flu" claimed one half million lives in the United States and as many as fifty million people throughout the world. Nearly half of the deaths were young, healthy adults. In 1957–58, "Asian flu" was responsible for seventy thousand deaths in the United States. The 1968–69 "Hong Kong flu" proved fatal for thirty-four thousand people in the United States. All three pandemics involved avian influenza, or bird flu. The 1957–58 and 1968–69 pandemics were caused by viruses containing a combination of genes from a human influenza virus and an avian influenza virus; the 1918–19 pandemic virus also appears to have been an avian flu.
Many scientists feel that it is inevitable that there will be another pandemic and that it is only a matter of time until the next influenza pandemic occurs. Although the severity of a future pandemic cannot be predicted, the CDC hypothesizes in "Pandemic Flu: Key Facts" that without effective vaccination against the flu or treatment for it, a "medium-level" pandemic in the United States could produce 89,000-207,000 deaths, 314,000-734,000 hospitalizations, 18-42 million outpatient visits, and another 20-47 million people being sick. Between 15% and 35% of the U.S. population could be affected, and the economic impact could be staggering—ranging from $71.3-$166.5 billion.
AVIAN INFLUENZA
Avian influenza is an infectious disease of birds caused by type A strains of the influenza virus. The disease, which was first identified in Italy more than one hundred years ago, occurs worldwide. Because these viruses usually do not infect humans, there is little or no immune protection against them. If an avian influenza virus infected people and gained the ability to spread easily from person to person, an influenza pandemic could begin. The first cases in humans probably resulted from contact with infected birds or surfaces contaminated with excretions from infected birds. The disease usually only affects birds and pigs; the first documented infection of humans occurred in Hong Kong in 1997. An outbreak of avian flu has affected bird populations in countries throughout Asia and Europe. It has affected humans as well—as of 2006 human cases of influenza A (H5N1) infection had been reported in Cambodia, China, Indonesia, Thailand, Vietnam, and Turkey.
The spread of H5N1 virus from person to person has been rare and as of June 2006 had not continued beyond one family living in close quarters in Indonesia. There is still, however, considerable cause for concern and vigilance, because the recent avian flu outbreaks in Asia and Europe have killed more than half of those infected. Even more frightening, most cases have occurred in previously healthy children and young adults as opposed to the old and infirm who generally succumb to influenza. 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.
PREPARING FOR A PANDEMIC
A vaccine is rarely available in the early stages of a pandemic. When a new vaccine against an influenza virus is being developed, scientists around the world work together to select the virus strain that will offer the best protection against that virus. Manufacturers then use the selected strain to develop a vaccine. Once a potential pandemic strain of influenza virus is identified, it takes several months before a vaccine will be widely available. For example, research to test a vaccine to protect humans against H5N1 virus began in April 2005, and clinical trials were underway in 2006.
Four different influenza antiviral medications (amantadine, rimantadine, oseltamivir, and zanamivir) are approved by the U.S. Food and Drug Administration (FDA) for the treatment and/or prevention of influenza. All four usually work against influenza A viruses. But the drugs are not always effective because influenza virus strains can become resistant to one or more of these medications. For example, the influenza A (H5N1) viruses identified in humans in Asia in 2004 and 2005 have proven resistant to amantadine and rimantadine, as has the seasonal flu strain that circulated in the 2005–06 U.S. influenza season ("CDC Health Alert: CDC Recommends against the Use of Amantadine and Rimandatine for the Treatment or Prophylaxis of Influenza in the United States during the 2005–06 Influenza Season," January 14, 2006, http://www.cdc.gov/flu/han011406.htm).
The U.S. Department of Health and Human Services (HHS) supports pandemic influenza activities in the areas of surveillance, vaccine development and production, strategic stockpiling of antiviral medications, research, and risk communications. In May 2005 U.S. Secretary of HHS Mike Leavitt created a multiagency National Influenza Pandemic Preparedness and Response Task Group. This initiative involves the CDC and public and private agencies at every level (international, national, state, local, and private) in planning for a potential pandemic. By early 2006 pandemic flu planning was underway—national, state, and local municipality programs, plans for businesses and schools, and advice for families and individuals. Prepared by the CDC, Table 7.4 outlines steps individuals and families can take to prepare for a pandemic flu, such as stockpiling nonperishable food and regular prescription medication.
On January 12, 2006, Leavitt announced $100 million in funding for state and local pandemic flu preparedness. This funding is part of $350 million included in the recent emergency appropriation for combating pandemic influenza passed by Congress in December 2005. Each state will receive a minimum of $500,000, with additional allocation of funds by population. States and municipalities will use these funds to accelerate and intensify current planning efforts for pandemic influenza. Current planning emphasizes practical, community-based procedures that could prevent or delay the spread of pandemic flu and help to reduce the burden of illness communities would have to manage during an outbreak ("HHS Announces $100 Million to Accelerate State and Local Pandemic Influenza Preparedness Efforts," HHS Press Office, January 12, 2006, http://www.hhs.gov/news/press/2006pres/20060112.html).
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