COVID-19 Vaccines – A Comparison

To date (January 2021) there are two COVID-19 vaccines authorized for use by the FDA in the United States under an Emergency Use Authorization.  A third is on the way. Here’s a quick comparison of the vaccines.

Before we talk about the vaccines themselves, it’s worth knowing about the new messenger RNA (mRNA) technology used to create two of them. In order trigger an immune response, older vaccines relied on injection of a weakened virus into our bodies. That’s not the case with mRNA vaccines. Instead, mRNA vaccines teach our cells how to make a piece of a protein that triggers an immune response. The antibodies produced during this immune response protect us if we come in contact with the SARS-CoV-2 virus that causes COVID-19 disease.

Pfizer Vaccine

Pharmaceutical giant Pfizer partnered with a German company, BioNTech, to create the Pfizer-BioNTech COVID-19 vaccine. This is an mRNA vaccine. According to FDA studies this vaccine is 95% effective.  This means that if the virus enters the body of a person who has already received the Pfizer vaccine, there is a 95% likelihood that this person will not become very ill.  Two doses of this vaccine are required, separated by 3 weeks.   It is approved for use in people age 16 and above.  The 95% effectiveness begins 7 days after receiving the second dose of vaccine.
The vaccine is manufactured in Michigan. It must be shipped and stored at -94 degrees Fahrenheit.  This is an exceptionally cold temperature that requires special freezer units. Vials may be placed in a regular refrigerator for up to 5 days. Once it is thawed to room temperature, it must be used within 2 hours.   The Pfizer vaccine must be mixed with saline (salt water) prior to injection. The special refrigeration requirements make this vaccine a little more difficult to use than the other vaccines.

Moderna Vaccine

Moderna is a biotech company founded in 2010. It was previously known as ModeRNA Therapeutics. This mRNA vaccine is 94% effective. Two doses are required, separated by 4 weeks.  It is approved for use in people age 18 and above.  The 94% effectiveness begins 14 days after receiving the second dose of the vaccine.
The Moderna vaccine is manufactured in Massachusetts.  It may be shipped and stored at standard freezer temperatures of -4 degrees Fahrenheit. Vials may be placed in a refrigerator for up to 30 days. Once it is thawed to room temperature it must be used within 12 hours. The Moderna vaccine is packaged ‘ready to use’ and does not require dilution.  Because it does not require a special freezer like the Pfizer vaccine requires, this is the vaccine you are most likely to receive at your doctor’s office or at a local pharmacy or large group vaccination site.

AstraZeneca Vaccine

Oxford University in England teamed up with the pharmaceutical company AstraZeneca to develop the Oxford-AstraZeneca vaccine. This vaccine was created using a genetically modified form of a virus that causes a common cold in chimpanzees. Scientists transferred the genetic instructions for the coronavirus spike protein to the this virus. As the vaccine enters cells in the body, this genetic code is used by those cells to produce the surface spike protein. This induces production of antibodies, resulting in protecting the body from infection by the coronavirus. In clinical studies, the AstraZeneca vaccine has been shown to be 70% effective.  Two doses are required, separated by one month.
The vaccine is manufactured in England, India, Norway, and Switzerland. It has not yet been approved for use in the US but is undergoing clinical trials. Unlike the Pfizer and Moderna vaccines, this vaccine may be shipped and stored at normal refrigerator temperatures between 36 and 48 degrees Fahrenheit. It may be stored at this temperature for up to 6 months. Because of the ease of shipping and storage, this vaccine may be much easier for use by pharmacies, doctors offices, and nursing homes than the other vaccines.

Side effects of the COVID-19 Vaccines

Side effects are similar between the Pfizer and Moderna vaccines. These include fever, headaches, and muscle aches. The side effects tend to be worse after the second injection than the first, and they tend to be more prominent in younger than older recipients.  Side effects of the AstraZeneca vaccine will be known once the clinical trials are completed.

Costs Per Dose

The vaccines have different costs, and this will ultimately also affect how they are used.  For instance, Operation Warp Speed made contracts with the companies for hundreds of millions of doses of their vaccines.  For each dose, the US government will pay AstraZeneca $4, Moderna $15, and Pfizer $20.  After government contracts phase out, Moderna will likely charge about $35 per dose.  Given the relatively minimal refrigeration requirements and low price of the AstraZeneca vaccine, it may be the vaccine distributed and used the most across the globe.


Both the Pfizer and Moderna vaccines contain polyethylene glycol and polysorbate. Anyone with an allergy to those should not receive the vaccines. Severe allergic reactions (anaphylaxis) have occurred in a few people who have received either of these vaccines. Because of this, caution is urged in people who have a history of serious allergic reactions.

More COVID-19 Vaccines

The American pharmaceutical company Johnson & Johnson has entered phase 3 clinical trials with their vaccine. GlaxoSmithKline has partnered with Sanofi to produce a vaccine, and the small biotech company Novavax is also developing a vaccine.

How Many Vaccine Doses Will The U.S. Have?

The U.S. government, through Operation Warp Speed, has contracts with the companies mentioned above for a total of 800 million doses of vaccine.  This number is more than the total number needed to provide two vaccinations for every person living in the United States in 2021.

Unanswered COVID-19 Vaccine Questions

The clinical trials have not yet provided answers to these questions:

  • Does receiving the vaccine prevent a person from being infected but not showing symptoms?  The effectiveness rates listed above show the percent of people who received the vaccine and did not become ill or show symptoms, compared to those who did not receive the vaccine.  The studies relied on reported symptoms, but did not measure those who did not have symptoms.
  • Can someone who has been vaccinated transmit the virus if they have the virus but do not have any symptoms?
  • How long do the vaccines provide protection?  This is not currently known.  It is possible that ‘booster’ immunizations will be required.
  • Are there potential long-term concerns?  The vaccines are authorized under the Emergency Use Authorization, but not formally approved by the FDA under its normal processes.  The clinical trials have shown that there are benefits to receiving the vaccines and the short-term risks are low.  Since the vaccines have not been studied over years, as would be the case in a normal FDA approval process, there is no long-term information on any of them.

As you can see, this comparison shows that each of the vaccines has advantages and disadvantages compared to the others.  If you go some place to be vaccinated, you probably won’t have a choice about which vaccine you will receive; they’ll use whichever vaccine they have.  I have always been of the opinion that a person should know what is being placed in her/his body, with the potential risks and the potential benefits.  Make sure to keep the information about which vaccine you receive in a secure location.  If it turns out that ‘booster’ immunizations are required, you’ll want to know which vaccine you received originally.

This blog was originally published on January 13, 2021, and updated on January 19, 2021.


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