COVID-19 vaccine ingredients explained

In this article we’ll explain what vaccines are made of, and what ingredients are in the COVID-19 vaccines that have been approved for use in the UK.
Coronavirus vaccine ingredients

What are vaccines made of?

The ingredients in the coronavirus vaccines are very similar to those used in other vaccines which make up the routine course of childhood vaccinations in the UK.

Many ingredients found in vaccines are also commonly found in some processed foods, and are used to preserve the vaccine and ensure that it works properly. Other ingredients you would find in a vaccine can also be found naturally in the human body, such as salt. The main ingredient in all vaccines is water.

Active vaccine ingredients are usually present in very small quantities. Each dose of the University of Oxford/AstraZeneca vaccine is 0.5 millilitres, and each dose of the Pfizer/BioNTech vaccine is 0.3 millilitres. The active ingredients in these vaccines amount to just a few thousandths of a gram.

Are vaccine ingredients harmful?

Although many of the ingredients would be harmful in large quantities (even salt is harmful if you consume a lot), they are present in vaccines in such minute quantities that they do not cause any harm to the human body.

There is no formaldehyde, aluminium or thimerosal in either the Oxford/AstraZeneca vaccine or the Pfizer vaccine. There is also no egg used.

A vial of the COVID-19 BioNTech/Pfizer vaccine. The Pfizer vaccine is made using mRNA technology. Photo: U.S. Secretary of Defence

What are the ingredients of the Pfizer vaccine?

The Pfizer coronavirus vaccine does not contain any live virus. These are the ingredients according to the UK government.

The active substance is BNT162b2 RNA

This is the synthetically engineered messenger RNA (mRNA), which is what teaches the body how to fight coronavirus. Traditional vaccines will present the body directly with a part of a virus molecule, or an inactivated or weakened version of the full virus, to teach the body how to create tailored antibodies. Unlike such vaccines, mRNA vaccine technology instead gives the immune system instructions on how to replicate a harmless piece of the virus molecule, by supplying it with the genetic instructions for this process. This process does not change any of the cells in your body.

Creative visualisation of SARS-CoV-2 virus particles. The Pfizer vaccine does not contain the live virus. Photo: National Institute of Allergy and Infectious Diseases (NIAID)


  • ALC-0315 = (4-hydroxybutyl)azanediyl)bis(hexane-6,1-diyl)bis(2-hexyldecanoate)

  • ALC-0159 = 2[(polyethylene glycol)-2000]-N,N-ditetradecylacetamide

  • 1,2-Distearoyl-sn-glycero-3-phosphocholine

  • cholesterol

The mRNA molecules are very fragile by nature, which is why they are enclosed in tiny fatty spheres that help protect them as they are injected into the body. ALC-0159 is the main ingredient of these spheres, while the others serve to stabilize the particles and help them maintain their structural integrity. These tiny spheres are extremely small cannot be seen by the human eye.


  • potassium chloride

  • potassium dihydrogen phosphate

  • sodium chloride

  • disodium hydrogen phosphate dihydrate

The Pfizer/BioNTech vaccine contains four salts, one of these (sodium chloride) is ordinary table salt. These work to keep the right pH (acid/alkaline) level in the vaccine to preserve its ingredients.


  • sucrose

Sugar is used in very small quantities as a stabiliser, to protect the active ingredient during manufacturing, transport, and storage.

The ingredients of vaccines are present in extremely small quantities, usually around a few hundredths of a gram.

Is mRNA technology safe?

Although this is the first time mRNA technology has successfully been used in a vaccine, it has been in development for over a decade, with many studies and trials taking place over the past few years.

MRNA vaccines present the body with a set of instructions to help it trigger creation of the antibodies to fight coronavirus. It cannot change the DNA of a human cell.

According to Jonas Nilsen, MD and co-founder of Practio "although this is the first time mRNA vaccines have been approved for use in the UK, mRNA technology has been studied and developed for decades. The development of an mRNA vaccine is a breakthrough that could result in vaccines being developed more quickly in the future.

Both the Pfizer and Moderna vaccines have been tested on tens of thousands of people, and have been proven to be both highly effective and safe."

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