What ingredients does Moderna’s COVID-19 vaccine have and how is it different from Pfizer?

The two most widespread vaccines in Western countries are based on messenger RNA technology, a small piece of genetic code, which allows our body to create antibodies against the new coronavirus. However there are differences in its composition.

The US federal drug agency, FDA, has published leaflets detailing the ingredients of each vaccine approved for emergency use in the COVID-19 pandemic. Many ingredients are similar but there are differences.

The European Medicines Agency has also published data on Moderna’s vaccine (PDF), after being approved on January 6, and the specifications of the one from Pfizer / BioNTech (PDF).

While most of the substances in the vaccine created by Pfizer and BioNtech are lipids and harmless salts, Moderna’s has other components. The difference lies in the method of preserving the formula. While Pfizer uses mainly salts, Moderna’s formula is acid-based.

The main ingredient: mRNA

It is the same principle as the Pfizer / BioNTech vaccine: messenger ribonucleic acid (mRNA), a revolutionary method that instead of inoculating an attenuated virus consists of recreating in the laboratory the genetic sequence of the “spike proteins”, the peaks used by the virus to invade our cells.

This synthetic information elicits a response from the immune system that “learns” to defend itself against this type of virus. It is considered less risky than inoculating a live virus.


Like the Pfizer / BioNTech vaccine, Moderna’s contains lipids that help preserve the delicate genetic code and transmit it to our body. The list presented by the FDA includes the following, most synthetics, used in microbiology.

[SM-102] Possibly heptadecan-9-yl 8 – ((2-hydroxyethyl) (8- (nonyloxy) -8-oxooctyl) amino) octanoate[PEG2000-DMG] 1,2-dimyristoyl-rac-glycero-3-methoxypolyethylene glycol-2000, a nanoparticle that facilitates assimilation Cholesterol (also present in Pfizer’s vaccine)[DSPC] 1,2-distearoyl-sn-glycero-3-phosphocholine a phospholipid used in other preparations.

Acid stabilizers

Tris (tromethamine), an amino used in preparations to balance acids The variant Tris HCl (tromethamine hydrochloride)


Acetic acid, in other words vinegar Sodium acetate, the salts of acetic acid


Sucrose, helps preserve particles

Herein lies the main difference with the Pfizer vaccine which mainly tries to regulate the PH thanks to salts instead of using acids. The objective in both cases is to regulate the acids so that the “king” of the vaccine, the mRNA, remains stable.

Moderna presented preliminary results with an efficacy of 94.5% against the new virus, similar to that of Pfizer / BioNTech. The sample in clinical trials was somewhat smaller with about 30,000 patients compared to more than 40 at Pfizer.

Moderna’s vaccine was developed thanks to the federal vaccine development program “Operation Warp Speed.”

One of the main differences between Pfizer’s vaccine and Moderna’s is that the latter does not require an extreme cold chain, which will facilitate logistical tasks. It can remain stable at between -30º and -20º C and last up to a month in a refrigerator. However, this vaccine is more expensive, in fact it is the most expensive, with € 31 per dose, compared to € 17 per dose for Pfizer’s. Between the two we find the Chinese Sinovac vaccine with € 25 per dose.

Another factor involved in logistics is that the minimum number of doses that can be distributed for Pfizer is almost 1,000, while Moderna’s vaccine can be distributed in much more manageable batches of 100 doses.

Both in Europe and the United States, the authorities have not given full authorization to the vaccines but rather an authorization for their “conditional” use due to the emergency due to the COVID-19 pandemic, considering that the benefits are greater than the risks to those that expose us these compounds.

Side effects

A key detail of the two vaccines, both Pfizer and Moderna (and most COVID-19 vaccines), is that they are reactogenic vaccines, that is, they cause a reaction in the immune system of the patient, so it is not surprising that they are more annoying than other types of vaccines.

On the other hand, as we pointed out, the experts consider mRNA vaccines easier to control because a virus is not being inoculated, but a synthetic genetic sequence.

The dreaded side effects are generally mild and pass in a few days, according to early reports.

The most common, for both vaccines, are injection site pain, fatigue, joint pain or headache, fevers or chills.

Young adults, with stronger immune systems, seem to suffer more side effects than older people. Side effects are more common after the second dose.

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