1. Influenza (flu)

2. The flu
The flu is a contagious infection of the nose, throat, and lungs caused by the influenza virus.
Causes
In temperate climates, influenza A usually arrives between early winter and early spring. Influenza B can appear at any time of the year.
The most common way to catch the flu is by breathing in droplets from coughs or sneezes.
Less often, it is spread when you touch a surface such as a tap handle or phone that has the virus on it, and then touch your own mouth, nose, or eyes.

3. Influenza virus Morphology:
Influenza virus particles are highly pleiomorphic (variable), mostly spherical/ovoid, many forms occur, including long filamentous particles
The outer surface of the particle consists of a lipid envelope from which project prominent glycoprotein spikes of two types:
haemagglutinin (HA)
neuraminidase (NA)
The inner side of the envelope
is lined by the matrix protein.

4. Types of virus Influenza A viruses
Infect a wide variety of mammals, including man, horses, pigs and birds.
The main human pathogen, associated with epidemics and pandemics.
There are 15 known haemagglutinin (H) serotypes and 9 known neuraminidase (N) serotypes.
Pigs and birds are believed to be particularly important reservoirs, generating pools of genetically/antigenically diverse viruses which get transferred back to the human population via close contact between humans and animals.

5. Types of virus
The serotypes that have been confirmed in humans, ordered by the number of known human pandemic deaths, are
H1N1, which caused Spanish Flu in 1918, and Swine Flu in 2009
H2N2, which caused Asian Flu in 1957
H3N2, which caused Hong Kong Flu in 1968
H5N1, which caused Bird Flu in 2004
H7N7, which has unusual zoonotic potential
H1N2, endemic in humans, pigs and birds
H9N2
H7N2
H7N3
H10N7

6. Types of virus Influenza B viruses Influenza C viruses
Infect mammals only and cause disease, but generally not as severe as A types.
Unlike influenza A viruses, influenza B viruses do not have distinguishable serotypes.
Influenza C viruses
This genus has one species, influenza C virus, which infects humans, dogs and pigs, sometimes causing both severe illness and local epidemics.
However, influenza C is less common than the other types and usually only causes mild disease in children.

7. Symptoms
Symptoms appear days later (usually within days). Because the flu spreads through the air and is very infectious, it often strikes a community all at once, causing an epidemic illness.
The flu usually begins suddenly, with a fever between 38.5 and 41 °C. (An adult typically has a lower fever than a child.)
The fever usually lasts for a day or two, but can last 5 days.
Other common symptoms include:
Body aches
Chills
Dizziness
Flushed face
Headache
Nausea
Vomiting

8. Symptoms
Somewhere between day 2 and day 4 of the illness, the "whole body" symptoms begin to subside, and respiratory symptoms begin to increase.
The most prominent of the respiratory symptoms is usually a dry cough.
Most people also develop a sore throat and headache. Runny nose (nasal discharge) and sneezing are common.
These symptoms (except the cough) usually disappear within days. Sometimes, the fever returns. The cough and tiredness usually last for weeks after the rest of the illness is over.
Other symptoms may include:
Loss of appetite
Muscle aches and stiffness
Stuffy, congested nose
Sweating

9. Possible Complications
Possible complications, especially for those at high risk, include:
Pneumonia
Encephalitis (infection of the brain)
Bronchitis
Sinus infections
Ear infections

10. Influenza vaccine
The seasonal flu vaccine protects against three influenza viruses that research indicates will be most common during the upcoming season.
The flu vaccine will protect against 2009 H1N1, and two other influenza viruses (an H3N2 virus and an influenza B virus(
The viruses in the vaccine change each year based on international surveillance and scientists' estimations about which types and strains of viruses will circulate in a given year.
About 2 weeks after vaccination, antibodies that provide protection against influenza virus infection develop in the body.

11. Influenza vaccine There are two types of vaccines: The "flu shot"
An inactivated vaccine (containing killed virus) that is given with a needle, usually in the arm.
The flu shot is approved for use in people older than 6 months, including healthy people and people with chronic medical conditions.
The nasal-spray flu vaccine
A vaccine made with live, weakened flu viruses that do not cause the flu (sometimes called LAIV for "live attenuated influenza vaccine"
Is approved for use in healthy people 2-49 years of age who are not pregnant.

12. Influenza vaccine When to Get Vaccinated?
Yearly flu vaccination should begin in September or as soon as vaccine is available and continue throughout the influenza season, into December, January, and beyond.
This is because the timing and duration of influenza seasons vary. While influenza outbreaks can happen as early as October, most of the time influenza activity peaks in January or later.
Who Should Get Vaccinated؟
On February vaccine experts voted that everyone 6 months and older should get a flu vaccine each year starting with the influenza season.

13. Influenza vaccine
While everyone should get a flu vaccine each flu season, it’s especially important that the following groups get vaccinated either because they are at high risk of having serious flu-related complications or because they live with or care for people at high risk for developing flu-related complications: 
Pregnant women
Children younger than 5, but especially children younger than 2 years old
People 50 years of age and older
People of any age with certain chronic medical conditions
People who live with or care for those at high risk for complications from flu, including:
Health care workers
Household contacts of persons at high risk for complications from the flu
Household contacts and out of home caregivers of children less than 6 months of age (these children are too young to be vaccinated(

14. Influenza vaccine Who Should Not Be Vaccinated
There are some people who should not get a flu vaccine without first consulting a physician. These include:
People who have a severe allergy to chicken eggs.
People who have had a severe reaction to an influenza vaccination.
Children less than 6 months of age.
People who have a moderate-to-severe illness with a fever (they should wait until they recover to get vaccinated.(

15. Influenza vaccine Vaccine Effectiveness Vaccine Side Effects
The ability of a flu vaccine to protect a person depends on the age and health status of the person getting the vaccine, and the similarity or "match" between the viruses or virus in the vaccine and those in circulation.
Vaccine Side Effects
Different side effects can be associated with the flu shot and LAIV.
The flu shot:
The viruses in the flu shot are killed (inactivated), so you cannot get the flu from a flu shot. Some minor side effects that could occur are:
Soreness, redness, or swelling where the shot was given
Fever (low grade(
Aches

16. Influenza vaccine The nasal spray LAIV
The viruses in the nasal-spray vaccine are weakened and do not cause severe symptoms often associated with influenza illness. In children, side effects from LAIV can include:
runny nose
wheezing
headache
vomiting
muscle aches
fever
In adults, side effects from LAIV can include
sore throat
cough