Influenza is a respiratory tract infection involving the upper airways and lungs. Many refer to influenza as the “flu”. Influenza is highly contagious transmitted by saliva and airborne droplets expelled by coughing and sneezing. The incubation is very short ranging from one to three days. Common symptoms of influenza are fever, chills, muscle aches and pains, dry cough, nasal congestion, sore throat, headache, malaise, fatigue, sneezing, sweating, and irritated eyes.

The influenza virus is an RNA virus that belongs to the orthomyxoviridae family. Three genera of the influenza virus currently exist. Each influenza virus is identified by the antigenic differences in their nucleoprotein and matrix protein.

The influenza B and C viruses infect only humans. Populations tend to have more resistance to these two viruses. This is because influenza B and C only undergo a type of evolution referred to as antigenic drift. RNA replication in these viruses is frequently error prone and leads to many point mutations. These point mutations lead to very little change in the new viral strain. Influenza B and C viruses cause relatively mild and limited disease epidemics. The influenza A virus infects mammals and birds (avian influenza). This virus is more likely to cause a pandemic (world wide epidemic). Influenza A is a recombinant virus, meaning an interchange of gene segments if two different viruses infect the same cell. This type of evolution is referred to antigenic shift. Avian and human strains recombining in pigs in the Far East may permit the virulent human strains to evolve. Common antigenic variants include H1N1, and H3N2.

Influenza A can be further classified by the surface proteins. Sixteen subtypes of the viral surface protein hemagglutinin (HA or H) currently exist. Nine subtypes of the viral surface protein neuraminidase (NA or N) exist. These surface proteins are essential for the virus’ life cycle.

The flu season reaches a peak prevalence in winter. The Northern and Southern hemispheres have winter at different times, meaning that there is actually two flu seasons annually. Two different vaccinations are made for the different flu seasons each year. The Northern Hemisphere flu season peaks in January or February. The Southern Hemisphere flu season peaks in October.

Influenza vaccines are developed each based off the predominant strains in the Southern Hemisphere. The vaccine contains an inactivated (killed) virus. Protection provided by the vaccine depends on effectiveness of the strain used to make the vaccine.

Vaccinations typically begin in October. Those that are susceptible to illness such as the elderly (65 years and older), young children (under 5 years of age), and immunocompromised patients are encouraged to be vaccinated. Young children are likely to get complications from the flu such as pneumonia, bronchitis, sinus and ear infections.

Anyone who has an allergy to eggs should not be vaccinated. Allergy to the vaccine is due to small amounts of egg protein that remain in the vaccine after purification. This is considered to be a rare side effect. Many complain of injection site soreness up to two days after vaccination. This is temporary and should go away. Typical side effects include fever, malaise, muscle aches occurring 6-12 hours after vaccination.

There are currently medications used to treat influenza. Amantadine and rimantadine are medications used to treat influenza A only. Neuraminidase inhibitors such as Tamiflu and Relenza block the normal function of the viral surface protein neuraminidase. These medications can be used to treat influenza A and B. Resistance to adamantine derivatives (amantadine, rimantadine) is seen in China, Hong Kong, Taiwan, and South Korea due to availability in over-the-counter remedies.

The avian flu naturally infects aquatic birds. However, pandemics occur when the avian adapted virus infects porcine (pigs). This virus will then recombine to form a genetically new virus. The genetically new virus infects humans that are in close contact with the infected porcine. The flu is then transmitted from person to person, beginning an epidemic.

In 1997 the avian flu (H5N1) originating from chickens in Hong Kong, killed 6 of 18 infected. This strain was not readily transmissible from human to human. However, this strain resurfaced in 2004 in Cambodia, Vietnam, and Thailand. This virus remains avian adapted and cannot be transmitted from person to person. A vaccine cannot be made until this virus has recombined into a human adapted form.

Elderberry extract is a trademarked over-the-counter remedy to shorten the duration of an influenza episode. This will not prevent the illness if taken before hand. Only vaccination can help to prevent influenza infections.

Influence is on the minds of many and rightfully so. The avian flu will pose a threat to the world's population if predictions are correct. Maintaining good health is essential during the flu season. One way to do that is take a good vitamin supplement.