shapoorfazli who is the seeker of Knowledge

What is influenza?

Influenza, commonly called "the flu," is an illness caused by RNA viruses that infect the respiratory tract of many animals, birds, and humans. In most people, the infection results in the person getting fever, cough, headache, and malaise (tired, no energy); some people also may develop a sore throat,nausea, vomiting, and diarrhea. The majority of individuals has symptoms for about one to two weeks and then recovers with no problems. However, compared with most other viral respiratory infections, such as thecommon cold, influenza (flu) infection can cause a more severe illness with a mortality rate (death rate) of about 0.1% of people who are infected with the virus.

The above is the usual situation for the yearly occurring "conventional" or "seasonal" flu strains. However, there are situations in which some flu outbreaks are severe. These severe outbreaks occur when the human population is exposed to a flu strain against which the population has little or no immunity because the virus has become altered in a significant way. Unusually severe worldwide outbreaks (pandemics) have occurred several times in the last hundred years since influenza virus was identified in 1933. By an examination of preserved tissue, the worst influenza pandemic (also termed the Spanish flu) occurred in 1918 when the virus caused between 40-100 million deaths worldwide, with a mortality rate estimated to range from 2%-20%.

In April 2009, a new influenza strain against which the world population has little or no immunity was isolated from humans in Mexico. It quickly spread throughout the world so fast that the WHO declared this new flu strain (termed novel H1N1 influenza A swine flu, often shortened to H1N1 or swine flu) as the cause of a pandemic on June 11, 2009. This was the first declared flu pandemic in 41 years.

Haemophilus influenzae is a bacterium that was incorrectly considered to cause the flu until the virus was demonstrated to be the correct cause in 1933. This bacterium can cause lung infections in infants and children, and it occasionally causes ear, eye, sinus, joint, and a few other infections, but it does not cause the flu.

What are the causes of the flu?

The flu (influenza) viruses

Influenza viruses cause the flu and are divided into three types, designated A, B, and C. Influenza types A and B are responsible for epidemics of respiratory illness that occur almost every winter and are often associated with increased rates of hospitalization and death. Influenza type C differs from types A and B in some important ways. Type C infection usually causes either a very mild respiratory illness or no symptoms at all; it does not cause epidemics and does not have the severe public-health impact of influenza types A and B. Efforts to control the impact of influenza are aimed at types A and B, and the remainder of this discussion will be devoted only to these two types.

Influenza viruses continually change over time, usually by mutation (change in the viral RNA). This constant changing often enables the virus to evade the immune system of the host (humans, birds, and other animals) so that the host is susceptible to changing influenza virus infections throughout life. This process works as follows: a host infected with influenza virus develops antibodies against that virus; as the virus changes, the "first" antibody no longer recognizes the "newer" virus and infection can occur because the host does not recognize the new flu virus as a problem until the infection is well under way. The first antibody developed may, in some instances, provide partial protection against infection with a new influenza virus. Unfortunately, almost all individuals have no antibodies that will recognize the novel H1N1 virus immediately. Consequently, without vaccination, the majority of the human population is susceptible to novel H1N1 flu.

Type A viruses are divided into types based on differences in two viral surface proteins called the hemagglutinin (H) and the neuraminidase (N). There are 16 known H subtypes and nine known N subtypes. These surface proteins can occur in many combinations. When spread by droplets or direct contact, the virus, if not killed by the host's immune system, replicates in the respiratory tract and damages host cells. In people who are immune compromised (for example, pregnant individuals, infants,cancer patients, asthma patients, people with pulmonary disease and many others), the virus can cause viral pneumonia or stress the individual's system to make them more susceptible to bacterial infections, especially bacterial pneumonia. Both pneumonia types, viral and bacterial, can cause severe disease and sometimes death.

Antigenic shift and drift

Influenza type A viruses undergo two kinds of changes. One is a series of mutations that occurs over time and causes a gradual evolution of the virus. This is called antigenic "drift." The other kind of change is an abrupt change in the hemagglutinin and/or the neuraminidase proteins. This is called antigenic "shift." In this case, a new subtype of the virus suddenly emerges. Type A viruses undergo both kinds of changes; influenza type B viruses change only by the more gradual process of antigenic drift and therefore do not cause pandemics.

A diagram that illustrates both antigenic shift and drift can be found athttp://www.medicinenet.com/swine_flu/page5.htm and shows how both mechanisms can lead to antigenically diverse virus strains. The U.S. Centers for Disease Control and Prevention (CDC) has indicated that novel H1N1 swine flu has an RNA genome that contains five RNA strands derived from various swine flu strains, two RNA strands frombird flu strains, and only one RNA strand from human flu strains. They suggest mainly antigenic shifts over about 20 years have led to the development of novel H1N1 flu virus.

Influenza (cont.)

What are flu symptoms?

Typical clinical features of influenza include

· fever (usually 100 F-103 F in adults and often even higher in children),

· respiratory symptoms such as

o cough,

o sore throat,

o runny or stuffy nose,

· headache,

· muscle aches, and

· fatigue, sometimes extreme.

Although nausea, vomiting, and diarrhea can sometimes accompany influenza infection, especially in children, gastrointestinal symptoms are rarely prominent. The term "stomach flu" is a misnomer that is sometimes used to describe gastrointestinal illnesses caused by other microorganisms. Novel H1N1 infections cause more nausea, vomiting, and diarrhea than the conventional (seasonal) flu viruses.

Most people who get the flu recover completely in one to two weeks, but some people develop serious and potentially life-threatening medical complications, such as pneumonia. In an average year, influenza is associated with about 36,000 deaths nationwide and many more hospitalizations. Flu-related complications can occur at any age; however, the elderly and people with chronic health problems are much more likely to develop serious complications after the conventional influenza infections than are younger, healthier people. However, the novel H1N1 virus has initially developed a different pattern of infection. Unfortunately, the pattern of infection is similar to that of the 1918 "Spanish flu" pandemic in which young people (pregnant individuals, infants, teens, and adults through age 49) are the most susceptible populations worldwide

What is the key to flu prevention?

Flu vaccine

Much of the illness and death caused by influenza can be prevented by annual influenza vaccination. Flu vaccine (influenza vaccine made from inactivated and sometimes attenuated [non-infective] virus) is specifically recommended for those who are at high risk for developing serious complications as a result of influenza infection. These high-risk groups for conventional flu include all people aged 65 years or older and people of any age with chronic diseases of the heart, lung, or kidneys; diabetes; immunosuppression; or severe forms of anemia. However, with the novel H1N1 flu, the CDC has listed these groups listed below as being at high risk and should obtain the novel H1N1 vaccine as soon as it is available to them:

· pregnant women,

· people who live with or care for children younger than 6 months of age,

· health-care and emergency-services personnel,

· people between the ages of 6 months through 24 years of age and children 5-18 years of age who have chronic medical problems, and

· people from 25-64 years of age who are at higher risk for novel H1N1 because of chronic health disorders or compromised immune systems.

Other groups for whom conventional flu vaccine is specifically recommended are residents of nursing homes and other chronic care facilities housing patients of any age with chronic medical conditions and children and teenagers who are receiving long-termaspirin therapy and who may therefore be at risk for developing Reye syndrome after an influenza virus infection. Influenza vaccine is also recommended for people who are in close or frequent contact with anyone in the high-risk groups defined above. These people include health-care personnel and volunteers who work with high-risk patients and people who live in a household with a high-risk person.

Because the flu is easily spread among children and because many children require hospitalization with the flu, the CDC now advises that all children 6-59 months of age receive a yearly conventional flu vaccination.

Are any side effects associated with the influenza vaccine?

Although annual influenza (injectable) vaccination has long been recommended for people in the high-risk groups, many still do not receive the vaccine, often because of their concern about side effects. They mistakenly perceive influenza as merely a nuisance and believe that the vaccine causes unpleasant side effects or that it may even cause the flu. The truth is that influenza vaccine causes no side effects in most people. The most serious side effect that can occur after influenza vaccination is an allergic reaction in people who have a severe allergy to eggs, since the viruses used in the vaccine are grown in hens' eggs. For this reason, people who have an allergy to eggs should not receive the influenza vaccine. Also, the vaccine is not recommended while individuals have active infections or active diseases of the nervous system. Less than one-third of those who receive the vaccine have some soreness at the vaccination site, and about 5%-10% experience mild side effects, such as headache, low-grade fever, or muscle cramps, for about a day after vaccination. These side effects are most likely to occur in children who have not been exposed to influenza virus in the past.

Nevertheless, some older people remember earlier influenza vaccines that did, in fact, produce more unpleasant side effects. Vaccines produced from the 1940s to the mid-1960s were not as highly purified as modern influenza vaccines, and it was these impurities that caused most of the side effects. Since the side effects associated with these early vaccines, such as fever, headache, muscle aches, and fatigue, were similar to some of the symptoms of influenza, people believed that the vaccine had caused them to get the flu. However, injectable influenza vaccine produced in the United States has never been capable of causing influenza because it consists of killed virus.

Another type of influenza vaccine (nasal spray) is made with live attenuated (altered) influenza viruses. This vaccine is made with live viruses that can stimulate the immune response enough to confer immunity but do not cause classic influenza symptoms (in most instances). The nasal spray vaccine (FluMist) is only approved for healthy individuals ages 2-49 years of age. This nasal spray vaccine contains live attenuated virus (less able to cause flu symptoms due to a designed inability to replicate at normal body temperatures). This live vaccine could possibly cause the disease in infants and immunocompromised people and does not produce a strong immune response in many older people. Side effects of the nasal mist include nasal congestion, sore throat, and fever. Headaches, muscle aches irritability, and malaise have also been noted. In most instances, if side effects occur, they only last a day or two. This nasal spray has been produced for both conventional and the novel H1N1 flu viruses and should not be given to pregnant individuals or anyone who has a medical condition that may compromise the immune system because in some instances the flu is the side effect. Caregivers should read the vaccine precaution insert before giving any vaccine, injectable or nasal, as these inserts are occasionally updated.

Some people do not receive influenza vaccine because they believe it is not very effective. There are several different reasons for this belief. People who have received influenza vaccine may subsequently have an illness that is mistaken for influenza, and they believe that the vaccine failed to protect them. In other cases, people who have received the vaccine may indeed have an influenza infection. Overall vaccine effectiveness varies from year to year, depending upon the degree of similarity between the influenza virus strains included in the vaccine and the strain or strains that circulate during the influenza season. Because the vaccine strains must be chosen nine to 10 months before the influenza season, and because influenza viruses mutate over time, sometimes mutations occur in the circulating virus strains between the time the vaccine strains are chosen and the next influenza season ends. These mutations sometimes reduce the ability of the vaccine-induced antibody to inhibit the newly mutated virus, thereby reducing vaccine efficacy. This commonly occurs with the conventional flu vaccines as the specific virus types chosen for vaccine inclusion are based on reasoned projections for the upcoming flu season. Occasionally, the vaccine does not match the actual predominating virus strain and is not very effective in generating a specific immune response to the predominant infecting flu strain.

Vaccine efficacy also varies from one person to another. Studies of healthy young adults have shown influenza vaccine to be 70%-90% effective in preventing illness. In the elderly and those with certain chronic medical conditions such as HIV, the vaccine is often less effective in preventing illness. Studies show the vaccine reduces hospitalization by about 70% and death by about 85% among the elderly who are not in nursing homes. Among nursing-home residents, vaccine can reduce the risk of hospitalization by about 50%, the risk of pneumonia by about 60%, and the risk of death by 75%-80%. If antigenic drift results in changing the circulating virus from the strains used in the vaccine, vaccine efficacy may be reduced. However, the vaccine is still likely to lessen the severity of the illness and to prevent complications and death.

The vaccine produced against the novel H1N1 swine flu was just initiated in the summer of 2009 and then rapidly tested for safety and effectiveness, in contrast to the longer time cycle used for production of conventional flu vaccine. However, the injectable (and nasal) vaccines used the same methods developed for conventional flu vaccines over many years. The expedited clinical trials for the novel H1N1 vaccines, according to the CDC, have shown the injected vaccine to be safe and very effective with immunologic protection developing in healthy people. In the 18-64 age group, 98% were protected while those over 65 were 93% protected. Other groups are being studied, but protection with the injected vaccine in preliminary and ongoing trials seems good, according to the CDC. To date, about 39,000 Chinese people have been given the vaccine with very few (four) developing only mild side effects such as muscle cramps and headache, according to WHO officials. Recently, data presented on the effectiveness of the nasal mist vaccine in adults were published; the data indicated that for conventional flu protection, the nasal mist was less effective than the injected vaccine in adults for the conventional flu. Other studies have shown that the nasal mist vaccine was slightly more effective in healthy children than the injectable vaccine. The following is a list of the CDC-approved H1N1 vaccines and the companies that name and manufacture them as of 10/29/09:

· Influenza A (H1N1) 2009 Monovalent Vaccine by Sanofi Pasteur

· Influenza A (H1N1) 2009 Monovalent Vaccine by Novartis

· Influenza A (H1N1) 2009 Monovalent Vaccine Live, Intranasal by MedImmune, LLC

· Influenza A (H1N1) 2009 Monovalent Vaccine by CSL Limited

shapoorfazli who is the seeker of Knowledge

Sunday, January 24, 2010

All informational links a bout influenza

Flu
(Influenza, Conventional and H1N1)

what is influenza ?

Influenza (cont.)

In this Article

What are flu symptoms?

Followers

kabul meidical faculty

medical university

shapoorfazli who is the seeker of Knowledge

Sunday, January 24, 2010

All informational links a bout influenza

Flu (Influenza, Conventional and H1N1)

what is influenza ?

Influenza (cont.)

In this Article

What are flu symptoms?

Followers

kabul meidical faculty

medical university

Flu
(Influenza, Conventional and H1N1)