There are different forms or types of flu shot vaccines having different ingredients, and routes of administration. All these vaccines are indicated by the age of the individual.

There are compelling reasons to take the flu vaccine every year. It is your best shot to prevent catching the flu.

A lot of research and effort goes into the formulating of the vaccines. This is because the flu has some serious complications and its epidemics and pandemics have caused a lot of deaths worldwide.

Besides the complications in adults, children can suffer more serious complications that can cause death 

Secondly, the influenza virus evolves or mutates every year and a new strain rides the air every season to infect the population. Vaccines are accordingly formulated and given to protect the people from the strains of the flu virus prevailing during the current season.

You can classify the influenza vaccine or the flu shot vaccine into various types by the following criteria:

A. By its route of administration: 4 types

  1. Standard intramuscular flu shot vaccine
  2. High-dose intramuscular vaccine
  3. Intradermal vaccine
  4. Nasal influenza vaccine called the Flu Mist


B. By its ingredients: 2 types

  1. The trivalent vaccine contains three components of dead viruses
  2. The quadrivalent vaccine contains four components of dead viruses

Types of flu shot vaccines by route of administration

There are four different types of flu vaccines classified according to how they are given. Each variety of the seasonal vaccine has its own use and indications.

All these four vaccines protect you from the three strains of the flu virus (trivalent vaccines), which are commonly seen prevalent in people:

  • Influenza B virus
  • Influenza virus type A (H1N1) viruses
  • Influenza A (H3N2) viruses

In 2012, the U.S. Food and Drug Administration approved the first quadrivalent vaccine, which offers you protection against four subtypes and strains of type A and type B viruses.

They include the three components of the trivalent vaccine plus an additional strain of the influenza virus B.

1) The standard intramuscular flu vaccine

The intramuscular flu shot vaccine, which is usually or traditionally used, contains dead flu viruses. Injection of the vaccine stimulates the immune system to produce antibodies that can fight off the live viruses, should they gain entry into the body.

The viruses in the vaccine are dead and hence, without any virulence, therefore, this vaccine cannot give you the flu.

The standard intramuscular influenza vaccine is made using viruses grown in eggs. Therefore, if you are severely allergic to eggs, you should take the vaccine in a doctor’s clinic or in a hospital.

However, the egg content of the vaccine is reduced and nowadays, CDC informs to say that there is no real danger for people with egg allergy to take this vaccine.

There are other vaccines available, which are manufactured without the use of eggs. Your doctor may advise you to opt for those.

The standard intramuscular flu vaccines are indicated for all people above the age of 6 months till the age of 64 years, including healthy people, people with chronic illnesses (such as asthmadiabetes, and chronic lung diseases), pregnant women, and people with high-risk careers such as health workers.

It is given deep into the deltoid muscle of the arm or in the anterolateral thigh muscle. The latter site also serves as the area of choice for infants and toddlers.

2) The high-dose intramuscular flu shot

The high-dose intramuscular type of flu vaccine contains a higher dose (four times the amount of antigens) of the same standard vaccine ingredients and is recommended for senior or elderly adults over the age of 65 years.

This helps to produce a stronger antibody response by the immune system. This compensates for the sluggish immune system, which has weakened due to aging.

You should know that a weakened immune system makes a person very prone to catching an infection.

According to a study published in The New England Journal of Medicine, the high-dose vaccine was 24.2% more effective in preventing flu in adults, 65 years of age and older as compared to the standard-dose vaccine.

The high-dose intramuscular vaccine is a trivalent vaccine. It is manufactured by Sanofi Pasteur Inc. and is sold under the brand name Fluzone High-Dose. However, it is also manufactured and sold by other manufacturers.

The Centers for Disease Control and Prevention gives an exhaustive list of vaccine manufacturers and their brand names. 

Though it is high-dosed, you need not have any apprehension in taking it, since it is safe. A few people may experience mild side effects such as pain and redness at the site of the injection, headache, muscle aches, and malaise. These effects disappear after one or two days.

3) The intradermal flu shot

The intradermal flu vaccine is a rather new vaccine introduced for the first time during the 2011-2012 flu season.

Its contents are similar to those of the traditional intramuscular shot and it is administered into the dermis or the skin. It uses a very small needle, 90% smaller than the one used for the intramuscular shot, which allows it to penetrate only skin deep. This vaccine is usually administered to the deltoid area of the arm.

The U.S, Food and Drug Administration (F.D.A.) approved Fluzone Intradermal for use in people 18 years to 64 years during the 2012-2013 flu season. At that time, it was a trivalent (three viruses) vaccine containing inactivated (or dead) viruses.

In the following year, The F.D.A. approved the quadrivalent form of Fluzone Intradermal, which is a quadrivalent vaccine containing the four inactivated viruses.

It is recommended for people in the age group of 18 to 64 years.

4) The nasal spray flu vaccine

The nasal spray vaccine or the Live Attenuated Influenza Virus vaccine (LAIV) does not contain dead viruses but live, weakened (or attenuated) viruses and is recommended for healthy people between the ages of 2 years to 49 years. It is sold under the brand name, Flu Mist and was first introduced in 2003.

This vaccine is contraindicated in high-risk individuals such as pregnant women, people above the age of 50 years, and those with chronic medical conditions. Though the virus is live, this vaccine cannot cause the flu because the virus is weakened and has a very low virulence that is easily tackled by the immune system.

The nasal-spray flu vaccine can cause mild side effects such as a runny nose, headache, sore throat, and cough. Children may develop a mild fever.

The nasal spray vaccine is sprayed into the nostrils by a needle-less syringe and does not require to be injected. Its advantage, therefore, lies in its painless delivery.

This makes it the vaccine of choice in children and people who would rather not be injected. This vaccine produces antibodies in the blood as well as in the nose, which is normally the virus’s point of entry into the body. The other vaccines produce antibodies in the blood only.

Studies indicate the nasal vaccine gives better results in the prevention of the flu in children as compared to injectable vaccines.

In adults, the injectable vaccines score over the nasal spray vaccines in the flu season.

CDC’s Advisory Committee on Immunization Practices (ACIP) now informs that the nasal vaccine should not be used during the flu season of 2016 – 2017. This is based on the data showing the poor or relatively lower effectiveness of LAIV (nasal vaccine) from 2013 through 2016.

Types of flu vaccines classified by ingredients

There is another method of classifying the influenza vaccine. According to this ingredient-based, classification, there are two types of influenza vaccines.

Trivalent flu vaccines are those that are effective against three types of flu viruses.
Quadrivalent flu vaccines are effective against four subtypes and strains of influenza viruses.

Trivalent flu vaccines

There are hundreds of influenza A-type viruses constantly mutating and difficult to predict. The A-type virus is the one that is responsible for epidemics and pandemics and for hundreds of thousands of deaths.

Against that, the type B virus has only two strains.

Trivalent flu vaccines are conventional vaccines that contain dead viruses and are administered by injection just before the start of the flu season.

They offer protection against the strains of the three viruses that are expected to infect during the flu season of the prevalent year.

These three viruses include the two influenzas A viruses (H1N1 and H3N2) and a strain of the influenza B virus, which can be either Massachusetts or Brisbane, depending on which is going to be prevalent during the current year.

Trivalent shots include:

  • Standard dose trivalent shots are approved for different age groups and administered through a syringe and needle into the arm. They contain egg protein because they are manufactured by growing the virus inside the egg.
  • The high-dose trivalent shot is indicated in people above the age of 65 years because they have a lowered immune protection due to aging.
  • The recombinant trivalent flu vaccine is approved for all adults above the age of 18 years. It does not contain egg protein and is hence indicated for those who are prone to egg allergy.
  • A trivalent flu shot vaccine containing an adjuvant stimulates the immune system into top gear and is ideal for people aged 65 years and older.

However, the trivalent vaccine is slowly being phased out and manufacturers are now more inclined to go in for the quadrivalent flu vaccines, which offer more comprehensive protection against four strains of the flu virus.

Quadrivalent flu vaccines

Besides the three strains of the flu virus against which the trivalent vaccine offers protection, the quadrivalent vaccine protects you from the second strain of the B virus not covered by the trivalent vaccine. That is the plus a B/Brisbane/60/2008-like (Victoria lineage) virus.

That means the vaccine offers protection against the two subtypes of the type A virus (H1N1 and H3N2) and both the strains of the B virus (B/Yamagata and B/Victoria).

Influenza B viruses are not divided into subtypes as is the case with influenza type A but are classified into lineages and strains. Currently, the two circulating influenza B viruses belong to either of its two lineages: B/Yamagata and B/Victoria.

The annual flu vaccine is manufactured covering the strains of the virus, which the scientists predict will hit the population that year.

There are different quadrivalent flu vaccines approved for different age groups.

  • There is one quadrivalent vaccine that can be given to children as young as 6 months of age.
  • Other quadrivalent vaccines are approved for individuals 3 years and older.
  • Then, there is the quadrivalent nasal vaccine approved for individuals between the ages of 2 years to 49 years. However, such individuals should not be associated with any contraindications to the nasal vaccines such as pregnancy, hypersensitivity to eggs, children on prolonged aspirin therapy, or compromised immunity.

In choosing your type of flu vaccine, your doctor can be your best advisor.