In the US, there are currently two approved COVID-19 vaccines to help with the fight against the current pandemic. Pfizer and Moderna both received Emergency Use Authorization (EUA) from the US Food and Drug Administration.
Pfizer is a widely known pharmaceutical company while Moderna specializes in biotechnology. The Pfizer vaccine received the authorization on December 11, while Moderna was authorized a week later on December 18.
Individuals belonging to the two high-risk groups recommended by the Centers for Disease Control and Prevention (CDC) will receive either of the two vaccines first: health care workers and residents of long-term care facilities in the country.
Both vaccines work against the same virus, and many more may possibly enter the market, so here’s a guide on the differences between the Pfizer and Moderna COVID-19 vaccines for your reference.
How do COVID-19 vaccines work?
Before we introduce the differences, it would be good to have a basic understanding on how these COVID-19 vaccines work.
All vaccines make it possible for your body to recognize and build a defense mechanism against COVID-19. None of them will actually give you the virus.
There are three main types of vaccines: vector, protein subunit, and mRNA vaccines. Pfizer and Moderna are messenger RNA or mRNA vaccines, a newer type of vaccine.
The CDC explains that mRNA vaccines use pieces of a spike protein found on the surface of SARS-CoV-2, the virus that causes COVID-19. These proteins spark an immune response in your body, creating antibodies familiar with fighting off future illnesses caused by the virus.
The protein and mRNA used to create that immune response are eliminated once they do their job. The antibodies will stay in your body and help protect you in the future.
A small amount of the virus is used for gene sequencing and vaccine testing but there are no viruses used to create the vaccine itself. This is its major difference from conventional vector vaccines, like the flu vaccine, which inserts genetic material from the virus into a weaker version of a live virus (different from the virus which it intends to fight) to help familiarize the body with the virus and prompt it to create specific antibodies for the next time it encounters that virus.
In an explanation provided by Pfizer, the RNA in mRNA vaccines instructs the body to produce antigens. As these antigens are presented to the body’s immune system, it prompts T-cell and antibody responses to fight the disease. The Moderna vaccine works the same way.
How effective are these vaccines?
Both the Moderna and Pfizer vaccines are most effective after completing the two doses. William C. Gruber, MD, senior vice president of Pfizer Vaccine Clinical Research and Development told The New York Times that their vaccine is 52% effective after the first dose, and it goes up to 95% after the second dose in individuals aged 16 years old and up. It has high efficacy regardless of one’s sex, age, and race.
Moderna, on the other hand, is about 94.1% effective against COVID-19. This is based on information reviewed by the FDA from a trial where Moderna tested the vaccine with 30,000 people ages 18 and up. There is a small difference in the efficacy of the two vaccines, but it’s not significant. They both work and do what they’re meant to do.
Are there any side effects?
Some minor side effects are to be expected, as is the case with any vaccine. The FDA provided a fact sheet with possible side effects for Pfizer’s COVID-19 vaccine:
- Injection site pain, swelling, or redness
- Tiredness
- Headache
- Muscle pain
- Chills
- Joint pain
- Fever
- Nausea
- Swollen lymph nodes
Pfizer also warns of a “remote chance” the vaccine could cause a severe allergic reaction within a few minutes to an hour after getting a dose. It is advised to have a risk assessment for the vaccine if you have had a history of severe allergic reactions. It is recommended that vaccines should be administered in a setting where medical treatment is available.
For Moderna’s COVID-19 vaccine, an FDA briefing document lists the following potential side effects:
- Injection site pain, swelling, or redness
- Tiredness
- Headache
- Muscle pain
- Joint pain
- Chills
- Fever
- Nausea/vomiting
There were no serious allergic reactions reported during the clinical trials, but the CDC and FDA will still recommend those with a history of severe allergic reactions to exercise caution when receiving the vaccine.
Ingredients of Pfizer and Moderna Vaccine
Pfizer and Moderna vaccine ingredients are both available to view online in a fact sheet. This is because both have been granted an EUA by the FDA.
The Pfizer vaccine contains the following ingredients:
- mRNA
- Lipids
- Potassium chloride
- Monobasic potassium phosphate
- Sodium chloride
- Dibasic sodium phosphate dehydrate
- Sucrose
Ingredients for the Moderna vaccine are listed as follows:
- mRNA
- Lipids
- Tromethamine
- Tromethamine hydrochloride
- Acetic acid
- Sodium acetate
- Sucrose
Each company has its own tweaks to its own vaccine, but they’re ultimately very similar. The mRNA does most of the work for the vaccine, lips help deliver the mRNA to the receiver’s body, and the other ingredients aid its stability and maintain the right pH.
Doctors from various hospitals agree they are essentially the same.
How are the vaccines stored?
The two vaccines must be stored in low temperatures but the Pfizer vaccine has to be stored at much lower temperatures. There’s a difference in the lipids composing the two vaccines and the Pfizer vaccine is less stable in warmer temperatures.
The Pfizer vaccine has to be shipped in specially-designed, temperature-controlled thermal shippers keeping temperatures at around -70 degrees Celsius (-94 degrees Fahrenheit). It can be stored for up to 10 days in those temperatures or stored in “ultra-low temperature freezers” for up to six months. Pfizer says the vaccine can also be stored for five days between 36 to 46 degrees in refrigeration units hospitals usually have.
The Moderna vaccine should be shipped at 20 degrees Celsius (-4 degrees Fahrenheit) and can stay stable in refrigeration units between 2 to 8 degrees Celsius (36 to 46 degrees Fahrenheit) for 30 days. The vaccine will stay stable at -20 degrees Celsius for up to 6 months, and up to 12 hours at room temperature.
How are they administered?
Each vaccine requires two doses given 21 days apart for Pfizer and 28 days for Moderna. The vaccine will specifically be injected into the muscle, typically the upper arm’s deltoid.
Overall, doctors advise that both vaccines and any vaccines that will get approved by the FDA are good and you must take whichever one you can.
QD Nurses supports the PPE Relief Initiative to help provide medical frontliners with complete personal protective equipment (PPE). Click here to know more about this project and the PPE Relief Initiative.
