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A Closer Look at the Pfizer and Moderna COVID-19 Vaccines

Updated: Mar 5

Author: Silvia DiPaola

Editors: Shamsia Ahmed

Artist: Tiffany Gao

After 9 months of the COVID-19 pandemic raging through the world, the light at the end of the tunnel has appeared in the form of vaccines. The two vaccines at the forefront were produced by the pharmaceutical companies Pfizer and Moderna. The Pfizer-BioNtech vaccine was authorized and shipped out to Americans earlier this week, and the Moderna vaccine is expected to be given emergency use authorization by the FDA as of December 18. However, what exactly are the differences between each vaccine, and what do they do?

There are a few technical differences between the two vaccines. For one, the Moderna vaccine can be stored in regular freezers and is not required to be transported in extremely cold transportation networks. It can be stored at -20˚C, which is the average temperature of a regular home freezer, and it can be kept in a refrigerator for 30 days before it expires. On the other hand, the Pfizer vaccine must be stored at -75˚C, and it is only viable for 5 days when placed in the refrigerator. It must be stored in expensive freezers with dry ice to maintain the frigid temperature. The Moderna vaccine involves 100 micrograms (mcg) doses 28 days apart while Pfizer’s is administered as 30 mcg doses 21 days apart. Lastly, Moderna’s would be used for people aged 18 and older, while Pfizer’s is authorized for use for those aged 16 and older. These differences highlight a notion that Pfizer’s vaccine is more practical for use in hospitals, while Moderna’s may be more useful in smaller communities, such as at local pharmacies.

Now, let's get into the similarities. Both Moderna's and Pfizer’s vaccines require two doses to achieve full immunity, and they both have a similar efficacy rate of approximately 95%. They also both rely on the use of mRNA (messenger RNA) to function. The side effects involved in both vaccines were very similar: injection site pain, fatigue, chills, muscle aches, low-grade fever, and headache were commonly reported with either type. These all highlight the development of an immune response, so these symptoms are nothing to fear. Lastly, they were both found to be equally effective in all races, ethnicities, and genders.

How do both vaccines function to generate an immune response? They both utilize synthetic mRNA, as aforementioned. mRNA is different from DNA in that the former directs the synthesis of proteins, while the latter contains the total genetic information of a cell. Scientists analyzed the genome of the spike protein on SARS-CoV-2 (the virus that causes COVID-19 infection) and synthesized synthetic mRNA to have the same genetic information as it. When the mRNA is introduced into your system, cells produce small amounts of this spike protein. However, the spike protein is not the actual coronavirus, which means your chances of becoming sick with COVID-19 are extremely low. Only the spike protein on the coronavirus will be introduced to your system. When your immune system detects this foreign body, it will start mass-producing antibodies to combat it. Finally, when the real SARS-CoV-2 virus comes into contact with your immune system, you will be ready to fight it off because you now have the antibodies specifically tailored to destroy it.

One of the main chemical differences in vaccines lies in the lipid delivery systems. There are fatty droplets involved (where the mRNA is located) that allow the mRNA to come into contact with your cells. However, these vary between the two vaccines, which is why the storage instructions are different for each.

Finally, are the COVID-19 vaccines safe? The consensus is: yes, the vaccines are safe. The FDA briefing illustrates that there are no specific safety concerns that would cause them to fail the emergency authorization process. Serious adverse events in the test subjects were highly uncommon, and no connection was established between them and the vaccine. The benefits are said to outweigh any possible risks such as contracting COVID-19 and having a severe infection.

The Pfizer and Moderna vaccines won't be available to the general public for several months, although there are a handful of healthcare workers that have been vaccinated or are planning on doing so. Now that you are aware of the biological facts of them, would you consider taking either COVID-19 vaccine when it is available?



Chow, Denise. “What Is MRNA? How Pfizer and Moderna Tapped New Tech to Make

Coronavirus Vaccines.”, NBCUniversal News Group, 18 Nov. 2020,

Levenson, Eric, and Jacqueline Howard. “What We Know about Moderna's Coronavirus

Vaccine and How It Differs from Pfizer's.” CNN, Cable News Network, 17 Dec. 2020,

Levenson, Eric, and Jacqueline Howard. “What We Know about Moderna's Coronavirus

Vaccine and How It Differs from Pfizer's.” CNN, Cable News Network, 17 Dec. 2020,

Lupkin, Sydney. “How Will Moderna Meet The Demand For Its COVID-19 Vaccine?” NPR,

NPR, 17 Dec. 2020,

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