Doing better this year:The influenza vaccination

Influenza is a contagious respiratory illness caused by influenza viruses. It can cause mild to severe illness and, at times, can even lead to death. In the United States, annual epidemics of influenza typically occur late fall through early spring. It is common to refer to these yearly winter epidemics as seasonal or interpandemic influenza. Sporadic, unpredictable pandemics can occur. There were three influenza pandemics in the 20th century.

Influenza viruses infect between 5% and 20% of the U.S. population annually. Approximately 36,000 influenza-associated deaths occur annually in the United States. More than 90% of these deaths involve people 65 years and older. Higher mortality occurs in seasons when influenza type A (H3N2) viruses predominate.

On average, there are 200,000 influenza-related hospitalizations annually. The highest rates of complications and hospitalization are among young persons and those 65 and older. Greater numbers of hospitalizations occur during type A (H3N2) epidemics. The economic impact of influenza is substantial, averaging $87.1 billion annually.

Annual vaccination is the most effective method for preventing influenza virus infection and its complications. The vaccine can be administered to any person six months or older, who does not have contraindications to vaccination, to reduce the likelihood of becoming ill with influenza or of transmitting influenza to others.

The effectiveness of the influenza vaccine depends, in part, on the match between the vaccine and influenza viruses that are circulating in the community. If these matches are close, vaccine effectiveness (VE) is high with values as great as 70% to 90% for inactivated vaccines. If the match is not close, VE is reduced.

A study in Wisconsin found an overall VE of 44% for the 2007-08 influenza vaccine. This included a 58% VE against the predominant influenza A (H3N2) strain and no effectiveness against influenza B viruses. No influenza A (H1N1) viruses were present in the population studied.

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Definition.

Influenza, commonly called "the flu," is an illness caused by viruses that infect the respiratory tract. Compared with most other viral respiratory infections, such as the common cold, influenza (flu) infection often causes a more severe illness with a mortality rate (death rate) of about 0.1% of people who are infected with the virus. Unusually severe worldwide outbreaks (pandemics) have occurred several times in the last 100 years since influenza virus was identified in 1933.

By an examination of preserved tissue, the worst influenza pandemic occurred in 1918 when the virus caused between 40 to 100 million deaths with a mortality rate estimated to range from 2% to 20%.

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 not the flu.

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Causes.

Influenza viruses 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 antibody against that virus; as the virus changes, the "first" antibody no longer recognizes the "newer" virus and reinfection can occur. The first antibody may in some instances provide partial protection against reinfection with an influenza virus.

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.

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Treatment and Prevention.

Treatment of Influenza

Typically, there is little that is done to treat the flu in otherwise healthy people.

Home Treatment

• Bed rest
• Drink extra fluids – at least one full glass of water or juice every hour.
• Acetaminophen (Tylenol), or Ibuprofen can relieve head and muscle aches. Aspirin should be avoided for children.

When To Call A Health Professional

• After three days of fever over 102 F.
• If cough brings up heavy mucus.
• If there is increasing difficulty in breathing.
• When a patient seemingly gets better, then gets worse again.
• If flu-like symptoms occur 10 days to three weeks after a possible tick bite because of the possiblity of Lyme's disease.

Finally, sometimes an anti-flu medication is necessary. Amantadine and rimantadine are effective anti-influenza drugs that can decrease the length of influenza-A infection by one-third if given within 48 hours of symptoms onset. They can also be used to prevent influenza-A infections. The most common side effects of these drugs are insomnia, nausea and dizziness.

Prevention of Influenza

Immunization against influenza provides fair protection, or may lessen symptoms if the disease is contracted. Every year, scientists develop a vaccine against the most recently circulating strain of the virus. The immunization is given by injection each fall in anticipation of the coming flu season.

You must be immunized within one week to four months prior to exposure for the shots to be effective. The vaccine is composed of inactivated organisms from several virus strains which scientists attempt to include the most recent mutation. Vaccines are typically 67 to 92 percent effective.

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