Influenza (which is a different disease from the similarly named disease Haemophilus Influenza type B) is a highly contagious virus disease with epidemics regularly occurring. Infection causes sudden onset of fever, chills, muscle aches, cough, headache, and may lead to pneumonia.

It is spread by sneezing, coughing or direct contact with the infected person.

Children and adults with long-term illness like asthmas and diabetes are more prone to serious flu complications such as pneumonia, dehydration, meningitis, and even death.

Influenza infection is a major cause of death in the elderly.
The virus has 3 subtypes A, B, and C.

Type A causes moderate to severe disease, affects only humans and affects all age groups.

Type B causes mild disease affects only humans, mostly children.

Type C affects animals and rarely humans and is not associated with epidemics.

The influenza virus also mutate frequently.

Antigenic shifts and drifts are major and minor changes in the antigens, or parts of the virus recognized by the body's immune system.
These changes allow the virus to persist in the population and give rise to epidemics of the flu.

Epidemics and Pandemics

Epidemics occur when incidence of influenza cases increase and mortality rises.

Pandemics occur with high incidence in all age groups and increased mortality.

Influenza pandemic could affect up to 200 million people with an estimated 400,000 deaths.

Sporadic outbreaks occur when clusters of cases occur in families, schools or small communities.

Influenza infections

The virus is acquired from respiratory droplets.

It replicated in the trachea and bronchi causing local destruction and is shed for 5-10 days.

Maximal communicatability occurs 1-2 days before onset and 4-5 days after.

Symptoms appear after an incubation of 1-2 days.

Abrupt onset of fever, muscle aches, non-productive coughs, and headaches occur.

Severity is less if the person has encountered a similar antigened virus before.

Only 50% of people have the above classical symptoms of influenza.

Symptoms last 2-3 days and rarely more than 5.

Aspirin should not be taken because of its association with Reye's syndrome, an often-fatal affliction

Complications of Influenza

Complications of the flu include pneumonia (either a bacterial superinfection on top of the influenza or an influenza pneumonia which is rarer). Reye's syndrome is a rare complication in children with the development of coma and brain swelling. Other complications include myocarditis (heart inflammation), and worsening of chronic bronchitis. Death occurs in 0.5-1 cases per 1000 cases, usually in ages >65 years.

Diagnosing influenza can be difficult and is largely on the clinical appearance along with its prevalence in the community. Influenza peaks between December and March in temperate climates but can vary. It is year long in the tropics and outbreaks are common aboard cruise ships.

Vaccination is done with an inactivated virus of circulating strains of type A and B influenza.

Egg protein is present.

The vaccine is effective in protecting 90% of healthy adults but only 30-40% of the elderly.

It is not highly effective in preventing illness but is effective in preventing complications and death particularly in the elderly.

The vaccine is most effective if given 2-4 months prior to flu exposure and is usually available in September. The vaccine may be given annually for people older than 9 years.

Children from 6 months to 8 years receiving it for the first time should receive 2 doses 1 month apart.
Flu shots are recommended for all people over 50 (over 65 are covered by Manitoba Health), children >6 months with chronic disease, long term care residents, health care workers, students, travelers, pregnant women, and persons 6 months to 18 years taking chronic aspirin therapy (so that they do not develop Reye's Syndrome).

Any person who wishes to decrease the likelihood of becoming ill from influenza should receive the flu shot although Manitoba Health does not cover all the above groups.

Adverse effects of the Flu Vaccine
Local reactions occur at the site if vaccination with soreness and redness lasting 1-2 days in 15-20% of people.

Non-specific fever and aches last 1-2 days in <1% of people.

Hives and allergic reactions occur rarely particularly in people allergic to eggs.

People with egg allergies should not receive the vaccine.

At present the flu vaccine is injected but a nasal preparation is being developed.

For people with flu like symptoms antiviral therapy is available with new drugs that can block viral replication and prevent illness if started as early as possible (within 48 hrs).

Vaccination still remains the best way of controlling the flu.

Influenza links

American Lung Association
Vaccine Information Statements