Moderna vaccine ingredients: What role does each part play?

Hand holding an injection Moderna vaccine (Image: Canva)

The long-standing wait for a coronavirus vaccine has seemingly come to end thanks to pharma giants Pfizer and Moderna’s timely endeavours.

Recently, there has been some debate about the ingredients in Moderna’s mRNA-1273, especially after a doctor from the US experienced an allergic reaction to it. For those of you are curious, here is a complete ingredient breakdown of the mRNA-1273 and what role each substance plays.

The COVID-19 vaccine called mRNA-1273 instructs the cells in the human body to make “spike protein” like that of SARS-CoV-2. The immune system then analyses it and makes antibodies to destroy it. So when the virus enters your body, your immune system already knows how to tackle it.

A single dose of the vaccine contains; messenger ribonucleic acid (mRNA), lipids (SM-102, polyethylene glycol [PEG] 2000 dimyristoyl glycerol [DMG], cholesterol, and 1,2-distearoyl-sn-glycero-3-phosphocholine [DSPC]), tromethamine, tromethamine hydrochloride, acetic acid, sodium acetate, and sucrose.

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Messenger ribonucleic acid or mRNA

Ribonucleic acid, according to National Human Genome Research Institute, is a single-stranded molecule similar to the DNA.

“The cell uses RNA for a number of different tasks, one of which is called messenger RNA, or mRNA. And that is the nucleic acid information molecule that transfers information from the genome into proteins by translation,” says Leslie G. Biesecker, M.D.

It started with isolating a virus from COVID infected person. Scientists sequenced the virus and documented its genetic information.

Moderna and NIH then identified the genetic sequence for the crucial spike protein on the surface of the coronavirus.

They encoded the information needed to create the spike protein into the mRNA.

Once you get the vaccine shot on your upper arm muscle, the human body cells make the spike protein piece, according to the information in the mRNA strand.

The cell then displays the protein piece, giving our immune system a chance to understand that it is a foreign body and build an immune response against it.

So when coronavirus enters the human body, the body recognises its spike protein and knows how to attack it. That’s because the mRNA vaccine has “trained” the immune system for it.

mRNA vaccines , therefore, don’t use attenuated or weak viruses in the vaccine. With just an mRNA strand, it “teaches” the body how to make a piece of protein, similar to that on the virus, helping the body create an appropriate immune response. 

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mRNA is the most important part of the vaccine and it should stay protected. In come the lipids, which form a wall of protection or an envelope around the RNA, preserving from any damage it could possibly face in the human body.

Lipid nanoparticles will mimic human cells so that it can travel inside the body with the RNA encased safely within.

These lipids are :

SM-102 – A proprietary ionizable lipid of Moderna, which is a primary ingredient to give structure to the lipid nanoparticle.

DSPC – A commercially available ionisable lipid that gives structure to the lipid nanoparticle.

Cholesterol – Cholesterol is an ingredient which human cell membranes are familiar with. The addition of the lipid will provide stability to the nanoparticle.

Polyethylene glycol (DMG-PEG 2000) – The lipid, like the others, help in the delivery of the mRNA efficiently. However, it has run into a little bit of controversy after scientists said that it could be responsible for causing severe allergic reaction in vaccine recipients.

All the four lipids come together as a lipid nanoparticle, which forms a wall around the mRNA.

Tris Buffer

The vaccine contains a combination of substances — Tromethamine, acetic acid, sodium acetate and sucrose – known as tris buffer. The buffer ensures that the ph of the vaccine stays closer to that of the human body (a slightly alkaline range of 7.35 to 7.45).

A combination of these ingredients in the Moderna vaccine helps in stabilising it.

Contrary to some beliefs, the vaccine does not contain microchips to track your information. Some also believed that the vaccine contains live viruses, which they thought, could cause COVID-19 in the recipients. mRNA also doesn’t enter the nucleus of the cell where the DNA is. The human body breaks down the mRNA after it retrieves the information from it.

For more info, check out the reference articles linked below.


1. Decoding Moderna’s Covid-19 Vaccine Ingredients
2. What Are the Various Ingredients in the COVID-19 Vaccines?
3. FDA Briefing Document Moderna COVID-19 Vaccine
4. Safety and Immunogenicity Study of 2019-nCov Vaccine (mRNA-1273) to Treat Novel Coronavirus
5.Understanding mRNA COVID-19 Vaccines