Flu or Influenza is an illness which is caused by the RNA virus. RNA virus affects the respiratory tracts of humans, birds and other animals. The virus causes an infection which results in high fever, severe headaches and cough. In some cases, it also results in nausea, diarrhoea, sore throat and vomiting. Most people deal with symptoms caused by the flu for one or two weeks and then get better with no issues. But, unlike most viral respiratory illnesses such as the common cold, influenza causes a very severe illness which has a 0.1% mortality rate or death rate.

Usually this situation occurs yearly and is known as seasonal or conventional flu. The flu season begins in October and continues till May. However, sometimes the flu outbreaks can be a lot more severe. This situation occurs when the population comes in contact to a flu strain to which they do not have immunity to. These outbreaks are known as epidemics. Many outbreaks have occurred in the history of the world. According to historians and researchers the worst outbreak occurred in 1918 and was known as Spanish influenza or the Spanish flu. The Spanish flu resulted in the deaths of around 40 million to a 100 million people all around the world. The mortality rate of the flu was thought to be in the range of 2% to 20%.

The difference between Influenza and a cold

Early symptoms of the flu may be the same as that of a cold but influenza weakens the body of patient with symptoms like fever, fatigue and congestion in the respiratory tracts. The flu is caused by type A, B and C of the influenza virus and their subtypes. The cold can be caused by so many different types of viruses. Cold symptoms are not life threatening and don’t last for a long time but influenza may cause a severe illness like pneumonia or can even result in death. Influenza or the flu symptoms also last longer and are more severe in nature. Fever and headaches are rare in the case of a cold, but they are common symptoms in the case of the flu. The flu can also result in severe chest pains for the patient. Swine flu can also cause diarrhoea and vomiting. Cold symptoms such as runny nose, cough with phlegm, congestion and slight fever are not dangerous and usually don’t last longer than a week.


The flu is caused by the influenza viruses. The influenza viruses have been responsible for many pandemics in the past 100 years. There are three types of influenza viruses:

Influenza virus A

Wild aquatic birds are the hosts to the influenza virus A, these viruses can be transmitted to other species and can causes many devastating outbreaks in the poultry or can also result in potential influenza pandemics in humans. This genus only has one species. The influenza virus A are the most dangerous out of the three types and have caused many severe diseases in humans throughout the years. A serotype or serovaris a distinct variation within aspeciesofbacteria or virusor amongimmune cellsof different individuals.The influenza virus A can sub divided into various serotypes based on the antibody responses to these viruses. The serotypes that have been found in humans are as follows:

1. H1N1 Virus that caused the worst outbreak in the recorded history also known as the Spanish flu in 1918 which resulted in estimated 40 million to 100 million deaths in the whole world with a mortality rate ranging from 2% to 20%. H1N1 virus also caused the outbreak of swine flu in 2009 which had a less than 0.1% mortality rate. H1N1 virus has the most recorded number of human deaths of all the influenza viruses.

2. H2N2 Virus that originated in China and caused the Asian flu pandemic outbreak. According to the World Health Organisation the Asian flu resulted in 2 million deaths worldwide.

3. H3N2 Virus was formed due to antigenic shift in the H2N2 Virus which resulted in a mild pandemic known as the Hong Kong Flu. The pandemic originated in Hong Kong and spread slowly to other parts of the world. Unlike, other pandemics the Hong Kong flu had a low death rate or mortality rate of 0.5%.

4. H5N1 Virus that caused the Bird Flu in 2004 is a deadly virus strain that is considered as the potential cause for a deadly worldwide outbreak in the future. However, as of yet the virus is not classified as a pandemic as it is not spread from human to human transmission. So far, virus was transmitted from birds to humans in all the cases.

5. H1N2 Virus is endemic to the human population and the pig and the bird populations.

The other serotypes include H3N8 virus that caused the Russian Flu in the late 1700s, H9N2, H7N2, H10N7, H7N3, H7N9 and H6N1 that affected only one person who recovered. This type of influenza virus is the deadliest and has a faster rate of spreading from one infected person to the other than the other types.

Influenza Virus B

Influenza Virus B is known exclusively infect humans. The only other animals that can be infected by this type of influenza virus are the ferrets and the seals. The genus only has one species and it is less common than the influenza virus A. The influenza virus B mutates at 2 to 3 times slower rate than that of influenza virus A. This type of virus is less genetically diverse and only has one serotype. Due to this lack of genetic diversity, humans usually acquire an immunity to the influenza virus B at an early age. Although, the influenza virus B mutates enough that permanent immunity is not really possible. The reduced rate of antigenic changes and close to no hosts for possible cross species antigenic shift ensures that there is no outbreak of influenza virus B pandemics.

Influenza Virus C

This genus has one species which infects dogs, pigs and humans. The influenza virus C is the least common type and can cause severe illness. However, it is less common than the other two types and usually causes mild sickness in children.

Antigenic Shift

Influenza Virus A goes through two types of changes, slowly over time mutation and gradual evolution which is known as the antigenic drift. The other type is known as the antigenic shift which occurs when two or more strains of the virus combine to form a completely new subtype. Influenza Virus A is the best-known example of this process, but this process occurs in other viruses as well. The cross-species antigenic shift is when the virus from one host species combines with the virus from another host species. Most influenza viruses spread through species to species transmission which cause a cross-species antigenic shift. For example, the H5N1 virus also known as the Avian Flu or the Bird Flu is transmitted from birds to the humans. The swine flu is caused by an antigenic shift in influenza virus found in the pig population. Because the human immune system has a problem recognising the new influenza virus strain formed by the combination of two strains it can result in a highly severe illness and possibly another pandemic.

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Symptoms of the flu

The flu will cause a high increase in the temperature of the patient’s body. The flu results in high fever unlike those caused by other respiratory infections. The temperatures from the fevers can range from 100°F (37.8°C) to 104°F (40°C). High fevers are more common in children than in adults but it is still an alarming issue and should be checked by the doctor. The symptoms caused by the fever include Chills and sweats. Usually, the fevers will last for three to four days.

A persistent and dry cough is a common symptom caused by the flu. The cough can get worse, painful and uncomfortable with time. The patient might also experience shortness of breath and discomfort in the chest. The cough caused by the flu can last up to two weeks. If the coughing causes a lot of pain in the chest it is advised to see a doctor and seek medical attention immediately.

Muscle and Body Aches
The flu cause muscles of the body to cause the pain. The flu pain occurs mostly in the neck, back, legs and arms. They might be severe which makes it difficult to move around and performing daily basic tasks.

Headaches are usually the first symptoms to occur in an individual when they contact the flu. The flu results in severe headaches, sometimes these headaches can also result in symptoms in eyes such as high sensitivity to light and sound.

The flu causes malaise which means tiredness or feeling like you have no energy in your body. This is a very common symptom in almost every disease. Feeling unwell is not necessarily a sign of having the flu. The fatigue or the feeling of tiredness usually comes on suddenly and fast. The feeling is very hard to overcome.

It is suggested to go to a doctor, to determine if the symptoms are caused due to a cold or due to the flu. There are a lot of rapid tests for the flu. Rapid Molecular Assay is a test conducted when an onset of three or more symptoms takes place. In this test, a nasopharyngeal swab or a nasal swab is used to take an upper respiratory tract specimen or a mucus specimen to determine the cause for the flu.


Influenza is a very serious virus that can cause many severe illnesses. It has a high rate of spread and even healthy people can be affected by it easily. Flu can even be deadly in some cases. The most efficient way to avoid the flu is to get vaccinated. Vaccinations also reduce the time a person is sick due to the flu and reduces the symptoms.

Flu Shots
Flu shots are the vaccinations used against influenza viruses. To make these vaccinations the scientists and researches choose the strains that they think will be the most common during the flu season. Once the vaccination is received the body starts producing antibodies to fight off the strains of the influenza virus. These vaccinations help in avoiding an infection from that strain of the virus in the future. Doctors advise that every person above the age of six months should be given flu shots. Especially those at a high risk such as pregnant women, adults over the age of 65, people with chronic diseases or weakened immune systems and children below the age of 5. It is suggested to get flu shots by the end of October to provide the body with the time to produce antibodies.

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Over the counter Medications

The over the counter medications are not as effective as vaccinations, but these medications help in reducing the symptoms and reduce the time it takes for the individual to get better. These medications help reduce the symptoms such as coughing (cough drops and syrups), congestion (decongestants) and dehydration. The medications or drugs such as Benadryl, Delsym and Sudafed or other oral fluids are given by the doctors for dehydration. Aspirin can be used in adults but not in kids. Antibiotics work against the bacterial infections and not viral infections like influenza.


There are side effects related to the flu vaccines, these side effects are mild and last only for a short duration of time. The side effects and complications last only for a day or two days at most. The side effects include soreness in the area where the flu shot was injected, a low-grade fever in the day following the vaccination shot, stiffness in muscles and mild pain in the muscles. Many people don’t even experience any of the side effects or complications. In some rare cases, the individual might have an allergic reaction to the flu shot. The doctors will ask the individual if they’ve had an allergic reaction due to medications or vaccinations before.

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Last updated on : 30-10-2018

Disclaimer : Docprime doesn’t endorse or take any guarantee of the accuracy or completeness of information provided under this article and these are the views strictly of the writer. Docprime shall not be held responsible for any aspect of healthcare services administered with the information provided on this article.

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