Flu Infection
About Flu

Flu is an acute infection of the bronchial tubes and is caused by the flu virus. Flu is extremely
contagious. Flu viruses spread in respiratory droplets caused by coughing and sneezing.
They usually spread from person to person. In addition, flu can have extremely serious
consequences. Every year in the United States, on average 5% to 20% of the population
gets the flu; more than 200,000 people are hospitalized from flu complications, and about
36,000 people die from flu.

A new human influenza virus in which the outer coating is drastically altered appears a few
times every century. This new virus can spread lightning-fast around the entire world. Such a
worldwide epidemic or pandemic can contaminate up to 50% or more of the world


Pandemic is a worldwide outbreak of influenza. It is different from a seasonal outbreak or
"epidemic" of influenza.

Seasonal outbreaks are caused by subtypes of influenza viruses that  already exist in human
population, whereas pandemic outbreaks are caused by new subtypes or by subtypes that
have never circulated among people or that have not circulated among people for a long time.

Examples of pandemics include:

Spanish flu, [A (H1N1)], caused the highest number of known influenza deaths: more than
500,000 American died, and up to 50 million people may have died worldwide.  [1918-1919]

Asian flu, [A (H2N2)], caused about 70,000 deaths in the US. First identified in China in late
February 1957, the Asian flu spread to the United States by June 1957. [1957-1958]

Hong Kong flu, [A (H3N2)], caused about 34,000 deaths in the United States. This virus
was first detected in Hong Kong in early 1968 and spread to the United States later that
year. [1968-1969]

Both Asian flu and Hong Kong flu were caused by viruses containing a combination of genes
from a human influenza virus and an avian influenza virus.

Pandemic are divided into interpandemic, pandemic alert and pandemic periods. In
interpandemic period, no new influenza virus subtypes have been detected in humans, but a
circulating animal influenza virus subtype poses a substantial risk of human disease. In
pandemic alert period, human infection(s) with a new subtype happens, but the spread is
localized. In pandemic period, increased and sustained transmission in general population

Why is Flu so contagious?

The outer coating of the influenza virus changes from time to time, making the virus invisible
to our antibodies that were built up during an earlier infection or vaccination. A slightly altered
virus can easily set off a new epidemic. Thus there is no lifetime vaccine against influenza
that lasts for a lifetime.

Flu Vaccination

Vaccination offers the most efficient protection to flu. In United States, October or November
is the best time to get vaccinated. The present flu vaccines are a mixture of multiple
vaccines, each offering protection to a certain virus strain. Vaccination reduces death and
the amount of hospitalizations as a result of flu considerably.

People at high risk for complications from the flu should get vaccinated. These include
people 65 years and older, people who live in nursing homes or other institutes, people with
chronic serious diseases, pregnant women and people in close contact with someone in a
high-risk group (e.g. caregivers and health-care workers).

How a vaccine works?

Each year the World Health Organization determines which influenza viruses are the most
likely to cause an influenza epidemic during the next winter period. Scientists grow viruses
on chicken embryos or in cultures of animal cells. They purify the proteins originating from the
outer coating of the harvested viruses and use it as vaccine. After inoculation in a human
body, the immune system creates antibodies. After a few weeks, our body has produced
sufficient antibodies to neutralize the viruses in case of an infection.

Antiviral Agents for Influenza

Four different influenza antiviral drugs (amantadine, rimantadine, oseltamivir, and zanamivir)
are approved by the U.S. Food and Drug Administration (FDA) for the treatment and/or
prophylaxis of influenza. All four have activity against influenza A viruses.

However, sometimes influenza strains can become resistant to these drugs, and therefore
the drugs may not always be effective. For example, analyses of some of the 2004 H5N1
viruses isolated from poultry and humans in Asia have shown that the viruses are resistant to
two of the medications (amantadine and rimantadine). Monitoring of avian viruses for
resistance to influenza antiviral medications is ongoing.


Current influenza vaccines work by targeting to haemagglutinin and neuraminidase on the
virus surface. These two proteins mutate from time to time. Acambis (a biotechnology
company in Cambridge) starts to develop a new vaccine targetingon different protein, M2,
that do not mutate, they hop it will be enough to offer permanent immunity against influenza.
Acambis has teamed up with the Flanders Interuniversity Institute for Biotechnology to
develop and license the flu vaccine.

PowderMed announced that it has progressed its H5N1 Avian influenza vaccine programme
into the final stages of preclinical development. PowderMed produces its H5N1 vaccine by
cloning the H5 gene from the current circulating avian flu strain into its DNA vaccine
backbone. They are ready to develop this vaccine, they plan to enter clinical trials by the
summer of 2006.

reference: British scientific team look for vaccine breakthrough that could offer human
immunity for life. Yorkshire Post Today. August 6, 2005. Vaccine Against H5N1 (Avian
Influenza) Manufactured for Clinical Development I-Newswire.com August 6, 2005.
Reference: Bird flu vaccine ordered, Newsday.com, August 9, 2005 [1] What's the Difference Between a Cold and the Flu?
Food Consumer.org September 13, 2009
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The first symptoms of a cold is getting a bit scratchy the first day, then the nose starts to run
on, followed by full blown sneezing and coughing on the fourth and fifth days, etc. It takes
several days for the common cold to get to full blown status.

Flu virus slams the patient to the ground with severe body aches, high fever, sore throat, and
coughs. While cold sufferers can limp along and actually function (albeit minimally), a flu
patient is rendered helpless. The difference comes down to intensity. Bacterial pneumonia,
which can be life threatening, is a very real threat to the flu patient; lungs, already severely
damaged from influenza, are susceptible to bacterial infection. The common cold patient's
problems are somewhat limited to sinusitis, bronchitis and otitis media (ear infections); none
of which are potentially fatal. [1]
On a dark-blue background, the illustration below provides a 3D graphical
representation (Credit: CDC.gov) of a generic influenza virion’s ultrastructure, and
is not specific to a seasonal, avian or 2009 H1N1 virus. A portion of the virion’s
outer protein coat has been cut away, which reveals the virus’ contents, and a key
has been included, which identifies these components.

There are three types of influenza viruses: A, B and C. Human influenza A and B viruses
cause seasonal epidemics of disease almost every winter in the United States. The
emergence of a new and very different influenza virus to infect people can cause an
influenza pandemic. Influenza type C infections cause a mild respiratory illness and are not
thought to cause epidemics.

Influenza A viruses are divided into subtypes based on two proteins on the surface of the
virus: the hemagglutinin (H), and the neuraminidase (N). There are 16 different
hemagglutinin subtypes and 9 different neuraminidase subtypes. Influenza A viruses can be
further broken down into different strains. Current subtypes of influenza A viruses found in
people are influenza A (H1N1) and influenza A (H3N2) viruses. In the spring of 2009, a new
influenza A (H1N1) virus emerged to cause illness in people. This virus was very different
from regular human influenza A (H1N1) viruses and the new virus has caused an influenza
pandemic. (Credit: CDC.gov)