The flu shot vaccine or the influenza vaccine ingredients include dead or inactivated viruses along with an adjuvant and certain additives and chemicals. Taking the vaccine reduces your odds of catching the flu by as much as 60%. That’s how effective it is.

The active flu shot ingredients in the vaccine, which include the dead or the live but weakened flu viruses, give you active immunization against influenza or the flu disease. They enable the body to produce antibodies against the virus, which keep you protected against the flu virus when you are exposed to it.

The flu virus evolves rapidly every year and new strains of the virus populate the air every flu season. These influenza vaccine contents or the ingredients are, therefore, changed every year to counter the changing properties of the virus.

Read about the flu virus and how it mutates to understand how the virus alters its properties every year and produces new strains against which the old vaccine becomes ineffective.

The Centers for Disease Control and Prevention (CDC) recommends that all individuals above the age of 6 months should take the flu vaccine.

Flu shot vaccine contents – List of ingredients

The main flu shot vaccine contents are the dead viruses, which when injected into the body activate the immune system of the body making it think an outside agent (the virus) has attacked the body.

The immune system produces antibodies to the antigen (dead viruses), which circulate in the body and offer protection against future attacks of flu.

The following is the list of the flu shot ingredients:

1. Aluminum as an adjuvant: Why is it added to the flu vaccine?

Aluminum salts act as adjuvants in the flu vaccine to boost your immune system into top gear.

An adjuvant is a safe substance added to the vaccine because it stimulates the immune system response and increases its effectiveness. This is particularly useful in elderly people, who have a weakened immune system due to aging.

An adjuvant also helps to reduce the amount of the antigen that is added to the vaccine.

Fluad is the first flu vaccine containing an adjuvant approved by the U.S. Food Drug Administration in 2015 for people 65 years and older. It has been in use in the United Kingdom for the last decade.

Fluad contains the adjuvant MF59, which is an oil-in-water emulsion of squalene oil.

The Swiss drug giant Novartis first researched and manufactured this vaccine. The Australian vaccine maker CSL purchased the product in August of 2015 and changed its name to Seqirus.

According to the Australian Technical Advisory Group on Immunisation (ATAGI),

” ATAGI does not recommend the use of this vaccine (seqirus fluvax) in children aged 5 to <9 years, unless an alternative vaccine is not available, as an increased risk of fever has also been demonstrated in this age group.”

2. Why is mercury (Thimerosal) added to the flu vaccine?

Additives like Thimerosal (mercury) are added in trace amounts to ensure the purity and stability of the vaccine. Thimerosal is primarily an ethyl mercury-based preservative used to prevent bacterial growth and acts as a preservative.

It is used only in multi-dose vials of the vaccine where needles have to be inserted multiple times into the vial to withdraw the vaccine into the syringe.

This can be dangerous since multiple insertions can introduce bacteria and other germs into the vaccine.

Thimerosal prevents the growth of microorganisms and fungi that can be possible contaminants. Thimerosal is, however, not used in single-dose ampoules.

3. Stabilizers

Every vaccine needs to be stable in its composition to maintain its potency during transport and storage.

Sugars and gelatin are added to the flu vaccine for the same purpose. They help to keep the vaccine effective during its entire shelf life.

Among all the influenza vaccine ingredients, gelatin is the biggest cause of allergy from this vaccine. It is known to cause allergic concerns in some children, but its number is very small. Its advantages far outweigh its disadvantages.

4. Formaldehyde

Formaldehyde is added to the flu vaccine during the manufacturing process because it acts as a deactivating agent. It kills the viruses and neutralizes the toxins released by the bacteria during the process of manufacture.

This protects the recipient of the vaccine from falling sick due to the vaccine.

Formaldehyde is a known carcinogen. Several studies have linked long-term formaldehyde exposure to certain types of cancer.

However, it is produced in the body and is essential for the production of amino acids. The formaldehyde is diluted several times during manufacturing leaving small residual amounts in the vaccine. The concentration in the vaccine is far below that, which is naturally present in the body.

At such concentration, it does not cause harm but serves well to act as a deactivating agent.

5. Egg proteins 

Egg-based manufacturing is the most common and old method used to make flu vaccines with killed viruses and vaccines with live weakened viruses.

The vaccine viruses are injected into the fertilized egg to allow them to replicate. They are then removed from the egg and killed for use in the vaccines as antigens after purification.

For the nasal spray flu vaccine, the viruses are not killed but weakened through a different process.

Due to this process, the vaccine does contain small amounts of egg proteins. However, not all influenza vaccines contain egg proteins.

Can you use the flu vaccine if you are allergic to eggs? According to Mayo Clinic, you can. But, a skin test would be in order, and in the case of a severe reaction, your doctor may prefer to give you the vaccine without the egg protein.

6. Antibiotics

Antibiotics are used in the manufacture of influenza vaccines to prevent the contamination of the vaccine by bacteria during the manufacturing process.

There need not be any concern that the antibiotics may cause a hypersensitivity reaction because those that do, such as penicillin, cephalosporins, and sulfa drugs are not used. Antibiotics that are used include neomycin, polymyxin B, streptomycin, and gentamicin.

Antibiotics are used

  • In some manufacturing processes to inactivate the viruses
  • To control bacterial growth in eggs during processing

Secondly, subsequent purification processes reduce their concentration to almost negligible quantities. As a result, they do not cause any allergic reactions.

Though some of the flu vaccine ingredients do have their potential dangers, it is their minuscule doses in the vaccine that keep them from causing harm. Additionally, there are compelling reasons why you should take the vaccine every year.

When should you take the flu vaccine?

You should take the vaccine just before the start of the flu season, which sets in during the months of the cold dry winter. It protects you for the whole season. People who are at a higher risk should particularly be careful not to miss taking the vaccine every year.

However, there is some controversy on whether elderly people above the age of 65 years and people whose immunity is compromised due to some health condition, should be advised vaccination twice during the flu season.

In the northern hemisphere (e.g. United States), the season starts in October and can extend to as late as May. It is at its peak during the month of February.

The CDC recommends that you should take the vaccine in the United States ideally before the month of October.

However, you can still take it later if you miss out on that. The protective effect of the vaccine starts fifteen days after you have taken the vaccine and can last in declining efficacy for a full 12 months. You stay well protected during the full flu season.

In the Southern Hemisphere, the season stretches from April to September. However, in the tropics, the influenza virus is active throughout the year.