As of February 27, 2021, three COVID-19 vaccines have been granted Emergency Use Authorization (EUA) by the U.S. Food and Drug Administration (FDA). The EUA allows faster access to medical products during a health emergency when no other approved options are available (Treatment, 2020). A breakdown of the three vaccines is shown below.

CompanyVaccine TypeDosesAgesEfficacy in preventing COVID-19**
Pfizer-BioNTechmRNA2 (3 weeks apart)12+95%
ModernamRNA2 (4 weeks apart)18+94%
Janssen (Johnson & Johnson)Viral Vector118+*67%
(updated as of 06/2021)

*The Janssen (Johnson & Johnson) vaccine has 67% efficacy in preventing moderate to severe COVID-19 disease. The Janssen vaccine has 85% efficacy in preventing severe to critical disease.

**These percentages are based on the results from the clinical trials used to study the vaccines.

Which Vaccine to Take

In general, individuals should receive whichever vaccine is available to them. There may be limited vaccine supplies and vaccine distribution locations may only offer one of the vaccines (Loftus, 2021). Consult your primary care physician if you have any questions about the vaccines or any concerns regarding allergic reactions. Anyone who has had a severe allergic reaction or immediate allergic reaction to any ingredient in any of the vaccines should not receive the vaccine. All three vaccines do not include eggs, latex, or preservatives (CDC, 2021c). Additionally, if individuals have a history of allergic reactions not related to vaccines, the CDC recommends that they get vaccinated. This includes people with allergies to pets, food, medications, and the environment (CDC, 2021d). More information about COVID-19 vaccines for people with allergies can be found here.

Side Effects

Common side effects for all three vaccines include pain, redness, and swelling at the injection site. Additionally, the three vaccines may cause other side effects such as tiredness, headaches, muscle pain, chills, fever, and nausea (CDC, 2021c). These side effects typically start within a day or two after receiving the vaccine. However, the side effects should go away after a few days.

Safety data shows that side effects were more common in individuals after receiving the second dose of either the Pfizer or Moderna vaccine. Safety data for the Janssen (Johnson & Johnson) vaccine shows that side effects were more common in individuals 18-59 years old compared to those 60 years and older (CDC, 2021c).

Difference Between mRNA and Viral Vector Vaccine Types

The Pfizer and Moderna COVID-19 vaccines are mRNA vaccines. mRNA vaccines teach our cells how to make proteins that trigger an immune response in our bodies, which can protect us from the real virus (CDC, 2021a). The Johnson & Johnson vaccine is a viral vector vaccine. This uses a modified version of a different virus to teach our cells how to fight COVID-19. The vector is a harmless virus and is not the same as the virus that causes COVID-19. Both types of vaccines cannot cause COVID-19 and do not affect DNA in any way (CDC, 2021b).

Efficacy of the Vaccines and What the Percentages Mean

Vaccine efficacy CANNOT be compared linearly. The three vaccines underwent different clinical trials and were tested at different times and locations. All three vaccines work well and have been granted EUA. The Johnson & Johnson vaccine has 67% efficacy against moderate to severe illness due to COVID-19 and has an efficacy of 85% in preventing severe or critical disease (U.S. Food and Drug, 2021b). In comparison, the flu vaccine is 40-60% effective and saves thousands of lives every year (Gavi, 2020). The COVID-19 vaccine should not be given within two weeks of other vaccines, such as the flu vaccine or a shingles shot (COVID-19 Vaccine, 2021). Receiving the vaccine is an important step in protecting yourself from COVID-19. Even after vaccination, wearing masks and washing hands will continue to be important safety measures.

Learn more about what it means to be vaccinated by visiting this article here.

Keiro supports the U.S. Department of Health and Human Services’ We Can Do This COVID-19 education campaign in efforts to increase education and awareness about the safety and efficacy of COVID-19 vaccines.

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CDC. (2021a). Understanding mRNA COVID-19 Vaccines. Retrieved from

CDC. (2021b). Understanding Viral Vector COVID-19 Vaccines. Retrieved from

CDC. (2021c). Different COVID-19 Vaccines. Retrieved from

CDC. (2021d). Information about COVID-19 Vaccines for People with Allergies.

COVID-19 Vaccine (2021). Retrieved from

Gavi. (2020). What is the difference between efficacy and effectiveness? Retrieved from

Loftus, P. (2021). J&J’s Covid-19 Vaccine: How Does the One-Dose Shot Compare with Others? What You Need to Know. Retrieved from

Olliaro, P. (2021). What does 95% Treatment. (2020). Retrieved from

U.S. Food and Drug. (2020). Pfizer-BioNTech COVID-19 Vaccine Frequently Asked Questions. Retreived from

U.S. Food and Drug. (2021a). Moderna COVID-19 Vaccine Frequently Asked Questions. Retrieved from

U.S. Food and Drug. (2021b). Janssen COVID-19 Vaccine Frequently Asked Questions. Retrieved from